Medical Oncology (1999) 16, 73-77 �9 1999 Stockton Press All rights reserved 07364)118/99 $12.00

REVIEW

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Mechanisms of polyclonal hypogammaglobulinaemia in multiple myeloma (MM)

Maria-Christina Kyrtsonis, Athanasia Mouzaki and Alice Maniatis

University of Patras Medical School, Laboratory for Hematology and Transfusion Medicine, Patras, Greece

Keywords: multiple myeloma; infections; hypogammaglobulinaemia; immunoglobulins

Introduction Polyclonal hypogammaglobulinaemia (immunoparesis) is the suppression of normal immunoglobulin (Ig) production and it reflects an impairment of humoral immunity, clinically expressed by a marked tendency of patients to develop gram-positive and gram-negative bacterial infections. The majority of multiple myeloma patients present with decreased polyclonal immunoglo- bulin production and although immunoparesis and infections constitute an important aspect of this disease, little is known about the mechanisms leading to humoral immunodeficiency.

Immunoparesis and infections: clinical observations in multiple myeloma and other mature B-cell neoplasms A decrease in normal Ig is a typical finding in MM patients and constitutes one of the minor criteria for the diagnosis of the disease, according to Durie's classification. Immunoparesis, however, is not specific for MM and is often seen also in B-CLL and in Waldenstrom's macroglobulinaemia. In all three dis-

Correspondence: Professor Alice Maniatis, University of Patras Medical School, Lab. for Hematology and Transfusion Medicine, Patras GR-26110, Greece. Tel: (3061) 999643/999644; Fax: (3061) 991991: E-mail: alcam@med.upatras.gr Received 1 December 1998: accepted 4 January 1999

eases, there is evidence that the primary antibody response is deficient since specific antibody titers against pneumococcus, tetanus and diphteria toxoids are reduced in patients, compared with healthy individ- uals. '-~ In addition, in all three diseases immunoparesis deepens in advanced stages. Surprisingly, however, extensive studies have not shown any strong correlation between the tendency to develop infections and the degree of immunoparesis 2 and even in patients with normal total Igs, a deficient specific antibody response to pneumococcal vaccine was found. In our experience, in MM, there is no statistical difference in the incidence of infections between patients with or without immuno- paresis and there is only a trend for the former. Consistent with these observations is the fact that although infections remain the most frequent cause of morbidity and mortality in both MM and B-CLL, immunoparesis per se is not considered an adverse prognostic factor for survival between patients within the same stage. A decrease in normal Igs might also be present in patients with MGUS (in 30% of cases); Gregersen et al found an association between MGUS and risk of bacteraemia although the overall risk was not statistically significantJ

The above observations suggest that the laboratory finding of decreased normal Igs reflects a varying impairment of humoral immunity that is most probably secondary, multifactorial and potentially reversible. Furthermore, the absence of immunoparcsis does not seem to exclude with certainty the presence of an underlying immunodeficiency in these diseases.

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Possible mechanisms involved in the induction of immunoparesis in MM The secretion of Igs in response to antigenic stimuli is a complex response, requiring the interaction of numer- ous cellular and humoral factors. In MM a variety of mechanisms have been implicated in the suppression of uninvolved Igs; among them are the effect of macro- phages, the decreased number of circulating polyclonal B-cells, the presence of suppressor B cells, the dis- turbed T cell control and the immunoregulatory role of cytokines.

Soluble immunosuppressive factors secreted by macrophages The first important finding that contributed to a better understanding of immunodeficiency in MM was made by Brother et al in 1975, who identified macrophages, from MM patients, that inhibit the production of polyclonal immunoglobulins in vitro. 5 Subsequently Kennard and Zolla-Pazner, using mice with plasmacy- tomas, suggested that myeloma cells produce a soluble factor (PC factor), that induces macrophages to secrete a second humoral factor, the plasmacytoma-induced macrophage substance (PIMS), which inhibits B-cell proliferation and Ig production. 6 These factors have not been well characterised. More recently, Farnen et al

characterised a new MM cell line, UMJF-2, which suppresses antibody production by B-lymphocytes in

vitro by secreting an immunosuppressive factor. 7 Whether the UMJF-2 derived soluble factor is analo- gous to the murine PC factor or PIMS is unclear.

Decreased number and function of B-lymphocytes The decrease in normal Ig production may be a result of suppression of normal B-cell differentiation. The abnormal B-cell maturation has been attributed to multiple factors such as increased CD5 + B cells that are immunosuppressive. 8'9 T cell mediated mechanisms and regulation by cytokines are discussed below.

There is also a suppression of B-cell progenitors that may be attributed to attrition of the normal plasma cell and B-progenitor cell compartment, in the bone mar- row and/or in lymph nodes, because both neoplastic cells and normal cells share the expression of the same adhesion molecules. 1~ Another possible mechanism of progenitor suppression is, that myeloma cell inter- action with stromal cells, leads to the secretion by both types of cells of factors that induce apoptosis in B-progenitor cells. 12

The suppression of B-progenitor cells in the marrow and plasma cell precursors in the peripheral blood has been documented by several recent studies with pheno- typic analysis, using flow cytometry, ira3 In the majority of the studies normal plasma cell precursors (CD19+38 +) in the blood as well as normal marrow B-cell progenitors, (CD19 § expressing CD5, CD10, CD34, CD38, CD45 l~ and Syndecam-1) decreased in patients with active disease. This phenomenon is reversible as shown recently by Rawston e t al . n In another study, Munshi et al observed improvements in B-cell function in MM patients who responded to therapy, with subsequent normalisation of their poly- clonal Igs) 4

The role of immunosuppressive cytokines In MM patients the levels of IL-4, a pleiotropic cytokine important for the induction of normal B-cell responses, were found significantly lower than in healthy individuals by Kawano et al. 15 In our study MM patients with active disease had lower levels of IL-4 which increased in remission. 16 IL-4 regulation may thus play a role in the suppression of normal plasma cell precursors, in active disease.

TGF-[31 is another cytokine which may play an important role in immunoparesis in MM. In a study of 35 MM patients in which serial measurements of serum TGF-~I were done, we found a strong correlation between serum TGF-~I levels and immunoparesis. 17 This finding suggests that normal polyclonal plasma cells are sensitive to the inhibitory action of TGF-~I on Ig production. Other investigators studying the possible role of TGF-~I in the suppression of normal B-cell populations, in plasmacytic neoplasms, found that the neoplastic plasma cells produced high levels of TGF-~I and that CD23, a marker of immature B-cells, was underexpressed in host B cells. CD23 underexpression was also observed when adding purified TGF-[31 to normal B-lymphocytes. 18 It has also been shown that TGF-~I acts by suppressing the phosphorylation of a retinoblastoma protein (pRB) which inhibits E2F transcription and causes cell growth arrest. 19 The suppression of pRB by TGF-~I derives from its upregulation of the p15 gene. 2~

The role of T cells Although MM is a B-cell malignancy, alterations in numbers, phenotype and function of T cells have been reported and may affect the immune system of the patients either directly, by disturbing the specific

Hypogammaglobulinaemia in myeloma M-C Kyrtsonls et al

cellular immunity or indirectly, because of inadequate cytokine production by T cells, affecting the prolifera- tion and differentiation of B cells.

Regarding T-cell function, in a study involving 14MM patients, isolated T cells cultured in vitro,

showed increased IL-6 production, when mitogenically stimulated with the lectin phytohemaglutinine (PHA), while their proliferative response was decreased. 2~ This decrease was reversed by the addition of exogenous IL-2 but not by exogenous IL-6 which may indicate a deficiency in IL-2 production. The possible role of IL-4 in MM has already been discussed.

These observations could be partially explained by the fact that the absolute number of T cells in MM patients is lower than in healthy individuals, with a marked decrease of the T helper population 22 and by

the finding that among the T helper cells there is a predominant reduction in CD4+CD45 + cells which represent an immature population. 23 On the other hand, the HLA-DR § T-cells are expanded, reflecting a state of activation induced by tumour growth. 24 These activated T cells are capable of producing large amounts of IL-2 and IFN-a but are unable to control the disease in vivo. 24 Massaia et a125 showed that T cells

in MM, which are activated in vivo, express an abnormal Fashigh/bcl-2 ~~ phenotype and hence are

more susceptible to apoptosis. In contrast, bcl-2 is overexpressed in the majority of MM B cells and this is likely to mediate their resistance to apoptosis induced by IL-6 deprivation or by certain drugs. 26 A recent study by Villunger et a127 showed that myeloma cells express on their surface the Fas ligand and actively destroy the T cells that express Fas upon activation: In their experimental system, blocking of Fas on the target cells or the Fas ligand on the tumour cells by receptor- and ligand-specific monoclonal antibodies respectively, protected T cells from being killed by the myeloma cells. These studies, taken together, show that T cells in patients are in a form of double jeopardy. When activated, as they should be, they are killed by their own phenotype as well as by the myeloma cells.

Increased catabolism of IgG In patients with IgG myeloma there is about a 2-fold increase in the rate of catabolism of both normal and clonal IgG because the IgG catabolism is directly proportional to IgG concentrations. The catabolic rate of other Ig classes is not affected. 2~

Supportive care of MM patients with functional hypogammaglobulinaemia and infections The range of microorganisms implicated in infections of myeloma patients varies, depending on the phase of the disease. Infections at disease presentation usually involve the respiratory system and are due to Strepto- coccus pneumoniae or to Haemophilus influenzae. The same micro-organisms plateau phase of the micro-organisms are immunity.

predominate in infections in the disease. Infections with these

typical of depressed humoral

When intravenous immunoglobulin (IVIg) became available a number of trials were undertaken in the hope that the administration of IVIg to myeloma patients would reduce their infection rate. One of the first studies by Schedel gave encouragement, since only 19.5% of patients receiving IVIg had infections, com- pared with 68% of those untreated) In a recent randomised study by Chapel et a129 the administration of IVIg as prophylaxis, in plateau-phase myeloma patients, resulted in a significant decrease in infections, compared with the placebo group ( P = 0.0002). Patients who benefited the most were those who had a poor IgG antibody response to immunisation by pneumovax.

The mechanism of action of IVIg is complex and is still under investigation. With regard to myeloma patients the protective action against infection could be attributed to boosting of antibody levels, especially in patients with severe immunoparesis. Another aspect worthy of study is the steroid sparing effect of IVIg through blocking of Fc receptors, since steroids are a sine qua non in the treatment of myeloma patients. More interesting, however, may be the effect of IVIg on the cytokine network, since a number of cytokines are implicated in the pathogenesis of myeloma as already mentioned. IVIg was shown to have an effect on cytokines and may also contain antibodies to cytokines and cytokine receptors. IVIg inhibits IL-4, TNF-a and IFN-y and induces anti-inflammatory cytokines (IL-1 receptor antagonist). 3~ 32 IVIg decreases secretion of IL-6 and TNF-R in in vitro experiments. 33 Finally, a recent study of IVIg administration to myeloma patients suggested that by reducing the rate of infec- tions, IVIg may play a role in improving survival. 3

Prevention of infections could be achieved also by the administration of antibiotics prophylactically. Results of recent studies are encouraging. 34'3~

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Conclusions The mechanisms leading to hypogammaglobulinaemia in myeloma are not yet fully uncovered. Further studies are under way by a number of investigators; they will hopefully lead to a better understanding of these mechanisms and will allow for correction of this defect, thus decreasing the incidence of infections in MM patients.

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