Do monoclonal antibodies and anticytokines still have a future in infectious diseases?

BIOLOGICAL RESPONSE MODIFIERS: I. Infectious Disease

Do Monoclonal Antibodies and Anticytokines Still Have a Future in Infectious Diseases? JONATHAN COHEN, M.B., F.R.c.P., London, United Kingdom, DIDIER HEUMANN, Ph.D., MICHEL-PIERRE GLAUSER, M.D., Lausanne, Switzerland

The continuing high mortality of septic shock has prompted a major effort by the research community to identify novel therapeutic targets. These targets can be conveniently grouped into (1) those derived from microbial components or products; (2) infiamma- tory mediators; and (3) effector molecules. Many of the experimental, so-called adjunctive agents developed have been monoclonal antibodies or anticytokine molecules of various kinds, and some have progressed into clinical trial. Unfortunately, these trials have failed to show unequivocal survival benefit for patients in shock, prompting a reappraisal of our approach to these agents. In this article, we discuss the possible reasons for these failures: (1) the targets are wrong; (2) the agents are inappropriate; or (3) the trial design is flawed. It would be premature to conclude that adjunctive agents have no future in the therapy of sepsis, but identifying the correct agent, and perhaps more importantly, the correct target population, is going to be more difficult than was at first believed.

M ost clinicians recognize septic shock as an illness associated with considerable morbidity

and substantial mortality. Examination of the placebo arms of the recent clinical trials in septic patients reveals that the overall mortality is generally 35-45%, although clearly this depends somewhat on the precise entry criteria. In the subsets of patients with established shock, the mortality rises alarm- ingly and may reach 65-X%. These figures trans- late to approximately lOO,OOO-300,000 deaths per year in the United States alone and? not surpris- ingly, during the last lo-15 years have been the stimulus behind a concerted research-based effort designed to try t,o improve the prognosis.

Despite the fact that gram negative bacteremia was the focus of most early work, examination of

the microbiologic findings in recent large studies in patients with sepsis reveals that a much broader approach is needed. The results in the placebo arm of two recent trials’?’ are shown in Table I. Al- though the investigators presented their data in slightly different ways, the results are remarkably consistent. Gram negative organisms account for only approximately 40% of the infections, and an almost equal number are caused by gram positive bacteria. Further, the single most common site of infection in both trials was the respiratory tract (36% and 27.4%, respectively); baeteremias ac- counted for only approximately 20%.

It became apparent some time ago that antimicrobial therapy alone was not an adequate response to the continuing high mortality of sepsis. Although the emergence of antibiotic resistance is certainly a major challenge and has been a particular problem in intensive care units, patients rarely die in septic shock because they are infected with a strain of bacteria that is resistant to the empirical therapy that had been chosen. Killing the bacteria is not the problem (indeed, some have suggested that it may contribute to the problem”). Rather, tissue injury appears to develop as a result of inappropriate host responses to a microbial stimulus. Thus, the main thrust of recent research has been to understand better the basic pathophysiology of sepsis and septic shock in order to try to identify new therapeutic targets.

The results have been spectacular, at least in terms of increased knowledge of basic science, We have learned, for instance, about the importance of natural endotoxin-binding proteins, such as lipo- polysaccharide binding protein (LRP) and the role of CD14 in activating cells. Many mediators have been identified, a start has been made on identifying signal transduction pathways and their regulatory proteins, and recognition of the potential role of effector molecules, such as nitric oxide, has opened up whole new areas of biology. As a result,

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TABLE I Distribution of Causative Organisms in the Placebo Arm of Two Recent Trials in Patients with Sepsis.

Anti-TNF Monoclonal Ab Percent by Patient

(n = 3301

Gram negative 38.9

Gram poshve 36.3

Mixed II.1

Anaerobes 1.6

Fung 5.4 Gthersiuaknown 6.5

= antlbody; NS = not stated; TNF = tumor necrox factor. ita taken from refs 111 and 121.

IL-1raTrial Percent by Organism

(n = 672)

39

378 NS

49 IOi

76

many possible therapeutic targets have indeed been identified, and strategies developed to evalu- ate their possible clinical value.

The number of potential adjunctive therapies now runs into the hundreds; they have recently been reviewed in detail.* The purpose here is not to be completely comprehensive, but rather to indicate the general approaches that have been taken and to pay particular attention to those agents that have already been in clinical trial, or are likely to be so soon. Among the earliest of these new agents to be investigated were neutralizing murine monoclonal antibodies and subsequently “humanized” or chimeric antibodies. For this reason, these new approaches to therapy were often loosely referred to as “immunotherapy,” but this is now probably inappropriate. Classic pharmacologic agents, such as platelet activating factor (PAF) antagonists and more recently nitric oxide synthase inhibitors, for instance, are clearly not “immunotherapeutics,” and therefore the more general term “adjunctive therapies” is now preferred.

THE SCIENTIFIC BASIS OF ADJUNCTIVE THERAPY The many different approaches to treatment that

have been considered can be conveniently (if somewhat arbitrarily) grouped under three headings: (a) methods that are directed at microbial targets; (b) a large group of treatments that target host mediators; and (c) a number of approaches that are directed, very loosely, against effector molecules.

Microbial Targets Bacteria produce a range of extracellular prod-

ucts and cell wall constituents that stimulate human immune cells in vitro to produce inflammatory mediators and that can independently trigger septic shock-e.g., illnesses in appropriate animal or human models. Perhaps the best characterized is gram negative bacterial endotoxin (lipopolysaccha-

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ride, LPS); its importance in initiating the sepsis syndrome has recently been reviewed.5 LPS binds to a number of different carrier molecules, the most important of which is LBP. The LPS-LBP complex is then able to interact with host monocytes via a cell surface molecule, CD14.” Interaction with other host targets, such as endothelial cells, that do not express CD14 on the cell surface is now known to be mediated by soluble CD14 molecules binding to the LPS-LBP complex and then interacting with- as yet unknown-cell surface molecules. In the case of gram positive bacteria, superantigenic bacterial toxins, such as staphylococcal toxic shock syndrome toxin-l (TSST-1) and streptococcal pyrogenic exo- toxin A (speA), can cause profound hypotension, inflammation, and organ failure in animal models.7 It is postulated that strains of Staphylococcus uu- reus and Streptococcus pyogenes that are able to express these toxins are the causal agents of staphylococcal and streptococcal toxic shock syndrome in humans. Superantigens are proteins that trigger T lymphocyte activation and proliferation via a non- specific interaction with both the Class II molecule of antigen presenting cells and a restricted reper- toire of T cell receptor variable p chains. Whereas a conventional antigen might interact with only a fraction of the hosts’ T lymphocytes, a superantigen can, in theory, interact with up to 20% of lymphocytes, triggering proliferation and massive release of pro-inflammatory cytokines.x*”

Inflammatory Mediators as Targets A great many inflammatory cascades are acti-

vated during sepsis, and many of them have been implicated as mediators of sepsis (Table II). Exper- iments in controlled conditions often suggest that blockade or neutralization of one of these cascades can prevent lethality, although many doubt whether these laboratory models are an accurate reflection of the complex situation found in the septic patient. Nevertheless, much effort has been spent in developing therapeutic strategies aimed at these inflammatory mediators.

The evidence that pro-inflammatory cytokines such as tumor necrosis factor (TNF)-cu and interleukin (IL)-1 play a causative role in the features of septic shock stems from several lines of research and has been reviewed elsewhere.“’ In brief: (a) natural or recombinant TNF-(Y and IL-l can induce features of septic shock in several animal models; (b) inhibitors of these cytokines can reverse the features of septic shock in animal sepsis models; (c) “knock-out” mice, deficient in the genes encoding receptors for TNF-LU, are resistant to septic shock induced by endotoxin; and (d) these cytokines are elevated in human septic shock and at least in some

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settings, levels of TNF-cu and IL-l correlate with poor outcome. Similar data suggest that most pro- inflammatory mediators produced by the host can, to some extent, exert deleterious effects and contribute to pathogenesis in septic shock.

Most mediators interact with specific receptors prior to initiating signal transduction in target cells. Families of receptors, such as those interacting with tumor necrosis factor-like ligands and the in- terleukins, are now recognized and have been cloned.” The discovery of these receptors opened up yet further opportunities for therapeutic intervention. Extracellular (“soluble”) TNF receptor was ligated to the Fe piece of an IgG molecule to improve its pharmacokinetics.” In the case of IL-l, the discovery of a naturally occurring receptor antagonist, IL-lra, led to a strategy based on inhibition by competitive receptor occupancy.‘” Finally, it emerged that modulating and anti-inflammatory mediators are released simultaneously with their pro-inflammatory counterparts, serving as coordi- nators and repressors of exaggerated immune responses. These counterinflammatory cytokines (such as IL-lo) are now being evaluated as therapeutic agents in their own right.i4

Although cytokines have been the focus of much work in this field, the importance of other mediator cascades should not be overlooked. Rradykinin is a peptide pro-inflammatory mediator that may be released during tissue damage and induces endothelial injury, activation of coagulation, hypotension, and stimulates cytokine release. Lipid mediators include platelet-activating factor and throm- boxane, prostaglandins, and leukotrienes.‘” Wide- spread activation of the coagulation pathways leading to disseminated intravascular coagulation is a serious complication of bacterial sepsis, and a number of treatment, strategies, directed at different components of the coagulationlfibrinolytic pathways, have been proposedi”

Multi-Organ Failure: Effector Molecules as Targets Hypotension and hypoxemia are pivotal in the

pathogenesis of multi-organ failure. Within the lung, cytokine-induced changes can lead to profound hypoxemia and respiratory failure. TNF-(u, IL-& and C5a all contribute to neutrophil chemo- taxis, whereas the upregulation of endothelial cell adhesion molecules and neutrophil integrins facili- tates the passage of fluid and leukocytes from the circulation into the interstitium and alveolar spaces of the lung. Acute inflammatory changes occur as a result of abnormal leukostasis and neutrophil de- granulation, leading to oxygen free radical- and enzyme-induced damage and, eventually, the acute respiratory distress syndrome (ARDS).

TABLE II Mediators of Sepsis.

Hlstamme Arachrdonlc acrd dewatrves Bradykw Endothelln Nltrlc oxide Complement

Kinins Platelet acttvatrng factor Cytokmes Endorphins Coagulahon factors

Reactive oxygen species

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Within the peripheral vasculature, TNF-a, IL-l, and interferon-y can synergistically trigger the production of nitric oxide (NO) in vascular smooth muscle cells. NO is a short-lived free radical, generated as a consequence of the conversion of r,-argi- nine to I,-citrulline by the enzyme nitric oxide synthase (NOS). NO is identical to the vasorelaxant endothelium-derived relaxing factor (EDRF) and exerts its actions by activating cyclic GMP.i7 Con- stitutive forms of NOS exist in endothelial cells and are concerned with the normal homeostatic control of blood pressure. It is thought that NO produced locally by inducible NOS (iNOS) within smooth muscle cells during septic shock contributes di- rectly to the refractory hypotension and vasoplegia often associated with this condition. Indeed, NO is a likely “final common pathway” to cytokine-mediated hypotension. Levels of plasma nitrate, a stable product of NOS activity, are elevated in patients with septic shock,” and inhibition of iNOS in TNF- treated animal models prevents the development of shock.“’ Perhaps the most persuasive evidence for the role of NO comes from the recent reports of mice in which the iNOS gene has been inacti- vated’“; in these animals there is a marked attenua- tion of the fall in blood pressure and reduction in the number of early deaths that occur in normal mice following LPS injection. However, the benefit of NO blockade has not been conclusively demonstrated in models of live bacterial sepsisal; indeed, it may even be harmful.2’

Myocardial depression and left ventricular dysfunction are recognized during the later stages of profound septic shock and has been attributed to a circulating myocardial depressant substance.2” Pro- found myocardial depression leads to worsening systolic hypotension in the septic patient and corre- lates with poor clinical outcome. Cumulative evidence suggests that the impairment of contractility seen during septic shock is related to circulating inflammatory cytokines. Recently, TNF-(U has been shown to reduce mammalian cardiac cell contractility by alteration of calcium influx. It is also apparent that cytokines such as TNF-cu and IL-1 can indi-

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rectly depress myocardial contractility through NO-dependent mechanisms. The source of NO in the myocardium is likely to be both endocardial and myocyte-derived.

The development of hypotension and hypoxemia as a result of vasodilation, cardiac dysfunction, and ARDS inevitably leads to acidosis and hypoperfu- sion within other tissues. The pattern of oliguria due to acute tubular necrosis, liver damage, and ischemie bowel necrosis is common to all forms of shock, septic or otherwise. The development of disseminated intravascular coagulation, leading to the deposition of fibrin and clot formation within small vessels, reduces tissue perfusion further. Multior- gan failure is associated with a very high mortality.

Clinical Experience ANTI-LPS ANTIBODIES: Because of the heterogene-

ity of multiple serotypes in gram negative bacteria, antibodies directed against the outermost O-antigen only provided homologous, but not heterolo- gous, protection experimentally. However, knowledge of the structure of endotoxin has allowed the generation of polyclonal and monoclonal antibodies against lipid A, the conserved part of LPS. Follow- ing very long debates on the precise molecular mode of action of polyclonal preparations against lipid A and the core region of LPS, two monoclonal antibodies (mAb)-HA-1A (Centocor, Malvern, PA) and Eli (Xoma, Berkeley, CA&--have been investigated in clinical trials.

The initial clinical trials were reported in 1991.“*,“” Both antibodies were expected to function similarly. However, whereas HA-1A was found to be beneficial only in patients with gram negative bacteremia presenting with shock at study entry, E5 was beneficial in patients with gram negative infection without shock. The results of these two trials generated an important debate regarding statistical validity and mode of action of the antibodies. Unfortunately, follow-up studies with both mAbs did not confirm the observations of the earlier trials [ref. 26, cited in ref. 41. HA-1A was withdrawn from the market and a thircl multicenter clinical trial with E5 is currently underway.

The lack of reproducibility of anti-LPS trials could reflect problems due to the heterogeneity of patients and to the complexity of the disease. How- ever, some biologic properties of the antibodies should also be considered. Although both antibodies bind to rough and smooth LPS, binding does not necessarily indicate neutralization. Two observations are pertinent in this regard: (a) neither mAb has been shown convincingly to neutralize LPS in the classic Lhdt~ assay; (b) neither mAb has been shown to reduce the pro-inflammatory

cytokine response mediated by LPS exposure to monocytes. These observations raise doubts about the therapeutic efficacy of these antibodies in humans. However the concept of anti-lipid A antibodies remains valid, and new antibodies able to neutralize LPS should be developed and investigated.

ANTI-TNF-(YANTIBODIES: 1. The CB0006 trial: In a phase II trial, 80 pa-

tients with severe sepsis or septic shock were enrolled to receive one of four dose regimens of anti- TNF-a MAb CB0006: 0.1, 1, 10 mg/kg, or 1 mgikg initially and a second dose of 1 mg/kg 24 hours later. No placebo group was investigated. Although survival estimates of all patients failed to demonstrate a survival advantage with increasing doses of CB0006, subgroup analysis of those patients with high TNF levels (>50 pg/mL) did suggest a benefit.27

2. The Bay x1351 trial (NORASEPT trial): Pa- tients with sepsis syndrome were enrolled, pro- spectively stratified into a shock and a nonshock group, and randomly assigned to receive either 15 mgikg or 7.6 mg/kg of anti-TNF-a mAb, or placebo. Interim analysis showed that among nonshock patients a slightly higher mortality rate was observed in patients receiving anti-TNF-a mAb. Thus, enrollment in the nonshock arm was discontinued. The final enrollment was 971 patients, with 49% in shock at study entry. Among all infused patients, there was no difference in all-cause mortality at 28 days in patients receiving placebo or antibody. Among septic shock patients, again there was no reduction in mortality at 28 days in patients receiving anti- TNF-a antibody versus placebo. However, a trend toward reduction of mortality was observed at 3 days (15 mg/kg: 44% reduction versus placebo, p = 0.01; 7.5 mg/kg: 49% reduction versus placebo, p = 0.004). In contrast, there was a nonstatistically significant trend toward increased mortality in nonshock patients who received 15 mg/kg anti- TNF-a mAb.

Two additional clinical trials with anti-TNF-cY antibodies are underway or currently being ana- lyzed. In the INTERSEPT trial with the Bay X 1351 antibody, there was a statistically significant effect on shock reversal and the development of organ/system failure, although this was not reflected in an overall survival benefit.” In the Knoll trial”’ with the murine antibody MAK 195 F, a ret- rospective analysis suggested that there was benefit in a subgroup of patients who had an elevated interleukin-6 level at the time of randomization, and a further trial is now in progress.

SOI,UBLE TNF KECEPTOK (:ONSTRUC'W A randomized, double-blind trial in patients with sepsis syndrome and hypotension was conducted with escalat-

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ing doses of sTNFR ~7’5 construct versus placebo.“” Inhibition of TNF-a with the ~75 construct was not effective in preventing death in patients at 28 days, and increasing doses of the construct were associated with increased mortality. A second clinical trial with another construct devised to inhibit the sTNFR p55 is under investigation.

IL.-I I~CEPTOR ANTAGONIST: Three clinical trials aimed at blocking the proinflammatory cytokine 11-l by means of 11-l receptor antagonist (IL-l ra) have been completed. In the preliminary trial, 99 patients with sepsis syndrome or septic shock were treated with placebo or escalating doses of IL-l ra.” A dose-dependent, 2%day survival benefit was associated with increasing doses of the drug, although the size of each treatment group was relatively small. A double-blind, phaSe III t.rial of 11-l ra in 893 patients with SIRS did not confirm the preliminary conclusions1 The overall mortality rate in patients receiving placebo was 34% whereas it was 29% in patients receiving high-dose 11-l ra. How- ever, a post hoc analysis suggested that survival advantage with 11-l ra was most apparent in a population of patients at intermediate risk of death. It was suggested that low-risk patients (~24% pre- dicted mortality) did not need the drug, whereas very high risk patients were beyond the point that they might benefit. To test this hypothesis, a further large clinical trial was begun, but when a planned interim analysis failed to show any likely benefit,‘W further development of the drug was stopped.

I’LAT~:I~1~;‘:‘r-ACTlVATINC; FA(!ToK ANTAGONIST: RN 52051, a PAF antagonist, was tested in a randomized, double-blind, placebo-controlled clinical study”” devised for treatment of patients with sepsis syndrome. Survival curves for the overall population did not show a statistical difference in mortality rates in recipients of placebo or active drug. However, the efficacy of RN 52051 in patients with gram negative sepsis was higher than the efficacy of the drug in other patients (I-, = 0.03). Further, the most severely ill patients benefited from PAF antagonist treatment more than the less severely ill patients.

This study raises the concern of failure of PAF antagonist treatment in patients with gram positive shock. I’AF is produced in response to both warn negative and gram positive bacterial products. PAF antagonists are known to uncouple various feed- back loops with cytokines, and it can only be specu- lated that mechanisms of cooperation between PAP and cytokine networks could vary according to the bacterial genus. Meanwhile, a follow-up trial that only enrolled patients with gram negative sepsis failed to confirm the findings of the first study.“”


HKAL~YKININ ANTAGONIST: A multi-center, rdn-

domized, placebo-controlled trial in patients with SIRS and sepsis has been conducted with CP-0127, a novel bradykinin antagonist.“” CP-0127 showed a positive dose-related trend in all patients in short- term survival that was much less pronounced at 28 days. In addition, CP-0127 showed a significant improvement in 2%day mortality in the subgroup of patients with gram negative infections. The drug appeared safe, since no excess mortality in any dose or risk group was observed.

Lessons from the Clinical Trials Despite great hopes, clinical trials conducted so

far in human sepsis have not been as encouraging as animal studies. Several causes may explain this rel- ative and perhaps temporary discouragement: (a) the design and the analysis of clinical trials of sepsis, or (b) the (lack of) relevance of animal models to study septic shock in humans.

PKOHLEMS RAISED BY THE 1)ESIGN OF CLINIt’AL

TIZIALS: Problems related to the design of the studies include (a) the selection of patients (broad re- cruitment versus narrow selection of well-defined infections); (b) the selection of endpoints (intent-to- treat analysis vs death from septic shock); (c) the existence of confounding factors (the decision not to resuscitate, the adequacy of surgical and medical treatment, or the presence of underlying disease). Such issues have certainly contributed to make the patient, population very heterogeneous, making it more difficult to judge the real efficacy of the drugs.

KELF;VANCE OF ANIMAL STIIDIES OF SEPSIS: The current strategy to attenuate the detrimental effect of cytokineslmediators in human sepsis was in fact mainly based on observations made in animal studies? which suggested that multiple organ failure is related to an uncontrolled systemic inflammatory state. Although in general anti-TNF-Lu and anti-IL- 1 therapies have shown a good degree of protection and an increased survival rate following parenteral injection of LPS or of bacteria in animals, no effect, or even a deleterious effect was observed in models of focal infections (especially peritonitis) with gram negative bacteria.“”

In animal models, the cascade of events starting from the initial stimulus and usually ending with the death of the animals follows most of the time a predictable time course. The resulting cytokine production also follows a predictable time course, and experimental approaches to block one cytokine cascade or another are relatively easy. In many animal models, the course of septic shock is usually hours or a few days. However, the sequence of events leading to septic shock in humans is more complex. The organisms and site of infections are

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very diverse, and importantly, the patients have a large variety of underlying diseases, which is not the case in animal studies. Moreover, most of the time the evolution of illness is more like days, rather than hours as seen in most animal models. For these reasons, it is extremely difficult to ex- trapolate to the clinical setting observations made in animal models.

When evaluating the potential efficacy of anticytokine/mediator strategies, a clear distinction emerges between models of parenteral bolus LPS or live bacteria versus models of focal infection. The parenteral models are perhaps more models of in- toxication than true models of infections. LPS or high bacterial inocula, lo!‘-10’” colony-forming units/kg, induce a brisk release of tosic cyt,okines that can be handled with blocking reagents. Impor- tantly, to be effective, the blocking agent must be given before cytokine release, a situation that is difficult to reproduce in humans. In contrast, in models of tissue infection, bacterial inocula are low; bacteria must multiply in order to invade tissues and eventually the bloodstream? and consequently the time-course of cytokine product.ion is different. Cytokine levels are low but, in contrast to parenteral models, are sustained during the whole obser- vation period. In fact, cytokine profiles in these models of tissue infection are very reminiscent of profiles observed in patients with shock, with both a low magnitude and a sustained production. The fact that anti-TNF-a therapies failed in these mad- els of focal infection or even worsened the prognosis, and the fact that TN&‘-a levels are low in these animals would favor the concept that TNF-cu does not play a toxic role in these conditions but rather helps fight infection.

The lessons from animal models were thus the following: (a) mediator blockade was efficient in parenteral models, provided blockade was done prophylactically; (b) mediator blockade in focal infections did not modify or even worsened outcome. In patients, although it is probably true that meningococcal purpura fulminans in children progresses in a fashion somewhat similar to that in animal models following parenterdl challenge, most patients have less acute infections, such as intra-abdominal infections or pneumonia, that may be present for several days before patients develop sepsis or septic shock, Clinical trials underway aimed at blocking the overproduction of cytokines in fact also suggest that such therapies could benefit the most severely injured patients, whereas they may worsen the less injured patients. A detailed analysis of these sub- @YU~S of patients would tell UP which animal models are more like human situations, The ability to identify this subset of patients early in the course of

clinical disease remains a critical challenge. We must develop methods that will allow us to shorten this delay in diagnosis in order to identify the patients that could benefit from these anticytokine therapies.

EXPLANATIONS AND THE FUTURE It must be acknowledged that the huge effort

that has been expended in the discovery and development of these novel agents has not yet been re- paid in a drug that unequivocally prolongs life. Why might this be? Several possibilities bear considera- tion.

The targets are wong; endotoxin, cytohkes, etc. aw mt as impodan t iu the pathogenesis of sepsis (xs /tie thought. This seems unlikely, based on the considerable amount of highly reproducible preclin- ical data. The evidence that LPS, inflammatory cytokines, and other mediator systems participate in the development of the sepsis syndrome seems secure. Many different experimental models have confirmed the findings, and they can be reproduced in humans, either in volunteers given LPS or in patients. Of course, to demonstrate that these mediators play a part in the pathogenesis of sepsis is not the same as showing that neutralizing or removing t,hem will necessarily be beneficial. One of the most difficult areas in this field is knowing which experimental models to use in order to predict efficacy in patients. Simply because an antibody protects ga- lactosamine-treated mice from lethal challenge with LPS does not mean that we can conclude that the antibody will be useful in clinical trials of sepsis. The situation is especially difficult at the moment because no single clinical trial has unequivocally demonstrated a survival benefit. Hence, no animal model can be “validated”; what we need is a drug that clearly works in a given model system awd works in patients. Until then, predicting clinical efficacy from animal trial data is impossible.

The dr~g.s that IKW~ heeu dvceloped aw iwf~ec- tive or inappopriatr. The cffi’ficacy of the drugs is generally not in doubt; anti-TNF antibodies really do neutralize TNF. However, perhaps they are being given inappropriately. For instance, a drug aimed at endotoxin is unlikely to be effective in infections caused by gram positive bacteria. We certainly cannot conclude that a drug active against one subgroup (say, gram negative bacteremia) will necessarily have broad applicability in all patients whom we currently lump together as “septic,” yet most recent clinical trials have approached patient enrollment in a rather nonselective way. We think of the entry criteria as having been rather “strict,” yet in truth they have resulted in a very heterogeneous population. Can it really be true that an 1%


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year-old patient with no relevant past medical his- tory who is admitted from the community with meningococcal shock has the (‘same” disease as a 71-year-old patient who develops a gram negative nosocomial pneumonia and septic shock while re- covering in hospital from major abdominal surgery? Another often-quoted example relates to timing: anti-TNF, for instance, is highly effective at preventing death in animals when given before the bacterial challenge, but fails if treatment is delayed. In patients, treatment is always “delayed” in that, sense, so perhaps anti-TNF is destined to fail for that reason.

7’/1r cl i?~,ica.l tl-iul desig?l is imppropviate, There is no doubt that we have been on a steep learning C’UIW so far as these trials are concerned. A simple comparison of the design of a trial of systemic ste- roids in sepsis, done more than 10 years ago, with one of the more recent studies shows clearly how much we have learned. Such issues as risk assess- ment, the importiance of the underlying disease, and the appropriateness of antimicrobial therapy are among many factors that we now recognize as having a major impact on outcome. Equally controversial is the question of outcome itself and how it should be measured. At present, 2%day all-cause mortality has been taken as the “gold standard”: only if this is significantly reduced is the drug re- garded as of any value. Is this a realistic goal? Are we (the academic community) and the regulatory authorities in danger of making a type II error: overlooking the possibility of a beneficial effect by making such stringent demands? Imagine, for instance, two experimental drugs, A and R. In phase III trials, neither alone prolongs 28-day survival, and both are in danger of being discarded (by the financial community, if not the academic one}. How- ever, an investigator then shows that drug A im- proves survival in the first 48 hours, during which time drug I3 has an opportunity to act, the net effect being a true reduction in 2%day mortality. Of course, clinical trials in such a setting are difficult to do, but we are dealing with a complex disease, and we should not necessarily expect simple answers.

It is to be hoped &at, all we have learned, both of the basic science of sepsis and its clinical evaluation, will before too long be reflected in better therapy for our patients.

From the Department of lnfectlous Diseases and Bacteriology, Hammersmlth Hospital and Royal Postgraduate Medical School, London, United Kingdom, and Department of lnfecbous Diseases CHUV Lausanne Switzerland

pi Requests for reprints should be addressed to Jonathan Cohen, M.B.. F.R.C.P.,

Department of lnfectlous Diseases and Bacteriology, RPMS, Du Cane Road, Lon-

- SYMPOSlUM ON CHEMOTHERAPY / COHEN ET AL

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Arch Intern Med 1992; 152: 1381-9. 17. Moncada S. Hlggs A. The L-arglnine-nltrlc oxide pathway. N Engl J Med 1993; 329: 2002-12. 18. Evans TJ, Carpenter A, KInderman H, Cohen J. Evidence of increased nltnc oxide production In pabents with the sepsis syndrome. Clrc Shock 1993; 41. 77-81. 19. Kilbourn RG, Gross SS, Jubran A, et al. N-methyl-L-arglnlne lnhlbits tumor necro- SIS factor-induced hypotenslon: impllcatlons for the Involvement of nitric oxide. Proc Natl Acad SCI USA 1990: 87: 3629-32. 20. MacMicking JD, Nathan C, Horn G, et ai. Altered responses to bacterral Infectron and endotoxlc shock in mice lacking Inducible nltrlc oxrde synthase. Cell 1995; 81: 641-50. 21. Evans TJ, Carpenter A, Silva AT, Cohen J. Inhlb!tloo of nitric oxide synthase In experimental gram negative sepsis. J Infect DIS 1994; 169: 343-9. 22. Fukatsu K, Salto H. Fukushlma R, et al. Detrimental effects of a nitric oxide synthase Inhibitor (N-w-nltro-L-arglntne-methyl-ester) In a murine sepsis model Arch Surg 1995; 130: 410-4 23. Parnllo JE. Burch C. Shelhamer JH, Parker MM, Natanson C, Schuetie W. A clrculat!ng myocardtal depressant substance In humans with septic shock. J Ckn invest 1985; 76: 1539-53. 24. Ziegler EJ, Fisher JCJ, Sprung C, et ai. Treatment of gram-negative bacteremta and septic shock with HA-IA human monoclonal antibody against endotoxln. A randomized, double-bknd, placebo-controlled trial. N Engl J Med 1991; 324: 429-36. 25. Greenman RL, Scheln RM, Martin MA, et al. A controlled chnical trial of E5 murlne rnonoclonal IgM antibody to endotoxln In the treatment of gram negative sepsis. JAMA 1991; 266: 1097-102. 26. Bone RC, Balk RA, Feln AM, et al. A second large controlled clmlcal study of E5, a monoclonal antibody to endotoxm: results of a prospective, multicenter, randomized, controlled trial Crtt Care Med 1995‘23: 994-1006. 27. Fisher JCJ, Opal SM, Dhalnaut JF, et ai. Influence of an anti-tumor necrosbs factor monoclonal antibody on cytoklne levels in patients with sepsis. Crlt Care Med 1993; 21.318-27. 28. Cartel J, Cohen J, Andersson J, et al. INTERSEPT: an rnternabonai efficacy and

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safety study of monoclonal anbbody to human tumor necrosis factor in pabents with the sepsis syndrome. (Abstr. B/l.) ICAAC 1994. 29. Reinhart K, Wergand-Lohneti C, Gnmminger F, Kaul M. Safety and efficacy of the monoclonal anti.TNF anbbody fragment MAK 19% in patients with sepsrs and sepbc shock. (Abstr.) Shock 1995; 3 (Suppll: 63. 30. Agostl JM, Fisher JCJ, Opal SM, Lowry SF, Balk JC, Sadoff JC. Treatment of patients with sepsis syndrome with soluble TNF receptor IsTNFR). (Abstr.) ICAAC 1994; 65: M4. 31. Ftsher JCJ, Slotrnan GJ, Opal SM, et al. inrtlal evaluation of human recombinant interleukin-1 receptor antagonlst In the treatment of sepsis syndrome: a randomized, open-label, placebo-controlled mulbcenter trial. Crlt Care Med 1994; 22, 12-21. 32. Fisher LM. Synergen halts tests: stock dives. New York Times 1995

33. Dhalnaut JF, Ten&on A, Le Tulzo Y, et ai. Platelet-activating factor receptor antagonist BN 52021 In the treatment of severe sepsis: a randomized, doubleblInd, placebo-controlled, multlcenter cllnical trial. Cnt Care Med 1994; 22: 1720-8. 34. Gourlay ML, Dhainaut JF, Tenalllon A, et al. Confirming phase III clinical trral to study the efficacy of a PAF antagonrst, BN 52021, in reducing mortality of patients with severe gram negabve sepsis. (Abstr.) Shock 1995; 3 (SuppI): 65. 35. Rodell TC, Scharschmldt LA, Knaus WA. Results of a multi-center, randomrred. placebo-controlled trial of CP-0127, a novel bradyklnin antagonist, in patients with SIRS and sepsis. IAbstr.1 Shock 1995; 3ISuppl): 60. 36. Bagby GJ, Plessala KJ, Wilson LA, Thompson JJ, Nelson S. Drvergent efficacy of antibody to tumor necrosis factor alpha in intravascular and perltonltis models of sepsis. J Infect Drs 1991; 163: 83-8.

Overview: Therapeutic Monoclonal Antibodies and Anticytokines in Infectious Diseases LOWELL S. YOUNG, M.D., San Francisco, CaIlfornia

T he occasion of the 19th International Congress of Chemotherapy in Montreal, Canada, pro-

vided the opportunity to assess one of the most complicated and controversial areas of clinical research over the last decade: the role of therapeutic monoclonal antibodies and anticytokines in infectious diseases. The enthusiastic response of the symposium attendees bears witness to the fact that, despite well publicized treatment t,rials that ended in failure? the medical public is still fascinated by the subject of new interventions for treating the sepsis syndrome and its sequelae. Professors Cohen and Glauser are to be complimented for the way in which they approached their subject: although the symposium was framed in the form of a debate, in fact, the position assumed by one speaker could well have been adapted by the other. In the preceding manuscript, they are joined by Dr. Didier Heu- mann; together these investigators provide a suc- cinct and very balanced review of the rational basis for these new interventions and why the human trials have disappointed clinicians in the field of infectious diseases and critical care medicine. I moder- ated this session and attempted to highlight the scientific issues. This introduction will not attempt to repeat the excellent points that have been made in the accompanying article. Suffice it to say that I agree that (a) there are major difficulties in extrap- olating the results of animal experiments to humans; and (b) the major practical challenges fol clinical field design relates to diagnosing the etiol- ogy of infection and promptly intervening.

Perhaps one f&or that overrides all others in evaluating outcome in trials of sepsis intervention,

particularly adjunctive therapies, is distinguishing the potentially reversible mortality from an infectious complication and the mortality associated with underlying disease. In other words, there is an “attributable mortality” that can be linked to leuke- mia or abdominal trauma. The mortality attributable to the infectious complication is likely to be only partly reversible. Perhaps the estimates have been too generous of the mortality attributable to the infectious complication. A corollary is that intervention trials, as reviewed by the authors, have failed to show a difference in survival because underlying disease is the paramount determinant of outcome. The role of underlying disease has been emphasized since the classic reviews of McCabe and Jackson more than three decades ago.’ Indeed, it was these pivotal studies that initially focused attention on the sepsis syndrome caused by gram- negative bacilli.

In designing new clinical studies, what should be the endpoints and outcome measures? If one has been looking for endpoints short of survival, the reversal of shock or hypotension might be one pa- rameter. However, as pointed out with the recent trials of anti-tumor-necrosis-factor antibodies, the findings of shock reversal have been inconsistent. We definitely need a more precise and rapid way of diagnosing gram-negative infection, because some of the interventions discussed will not work for gram-positive, fungal, or viral causes of the sepsis syndrome.

Any large clinical studies that are undertaken in the future are likely to benefit from implementation of more uniform antimicrobial treatment protocols.

6A-52s December 29, 1995 The American Journal of Medicine Volume 99 (suppl 6A)

Documents

Do monoclonal antibodies and anticytokines still have a future in infectious diseases?