The T cell activation molecule H4 and the CD28-like molecule ICOS are identical.

The recently cloned CD28-like molecule ICOS displays striking similarities with H4, characterized some years ago in the mouse and recently in humans. Both molecules are selectively expressed by activated and germinal center T cells, display similar structure, and display co-stimulatory activities. H4 displays lateral association with the CD3/TCR and is expressed by mature thymocytes. In the mouse, H4 is also expressed at high levels by thymic NKT cells that are resistant to negative selection. The aim of this work was to evaluate whether H4 and ICOS are the same molecule using the C398.4A (binding human and mouse H4) and F44 (binding human ICOS) monoclonal antibody (mAb) in parallel experiments on human T cells. ICOS and H4 displayed the same expression pattern in a panel of T cell lines and the same expression kinetics in phytohemagglutinin-activated T cells. C398.4A completely blocked cell staining by F44, whereas F44 partially blocked C398.4A. H4 and ICOS immunoprecipitates displayed identical SDS-PAGE patterns and H4 immunoprecipitation completely removed ICOS from cell lysates. Finally, the C398.4A mAb specifically stained cells transfected with the human or mouse ICOS. These data prove that H4 and ICOS are the same molecule and that F44 and C398.4A bind partially different epitopes.

Characterization of a novel human surface molecule selectively expressed by mature thymocytes, activated T cells and subsets of T cell lymphomas.

We have previously characterized mouse H4 (mH4), a surface glycoprotein recognized by the C398.4A monoclonal antibody. We now show that C398.4A also binds its human putative homolog (hpH4). Both hpH4 and mH4 (1) are selectively expressed by activated T cells and mature thymocytes, (2) are disulfide-linked dimers of two chains (29/37 kDa in humans, 25/29 kDa in mice), whose N-deglycosylation produces a single band at 20 - 21 kDa, and (3) display a low association with CD4 and the TCR. The expression pattern of hpH4 and its biochemical features showed that it is different from other known activation molecules, and this was confirmed when analysis of the tryptic digest of the hpH4 29-kDa band by peptide mass searching using matrix-assisted laser desorption ionization mass spectrometry did not reveal any significant homology with other molecules. In normal lymphoid tissue, hpH4 is expressed by T cells located at the periphery of lymph node germinal centers and paracortical areas. In T cell neoplasia, expression of hpH4 clusters with a subset of peripheral T cell lymphomas with a large-cell component, and with cases of angioimmunoblastic T cell lymphomas. Overall, these data provide evidence for a novel T cell activation molecule that could help in the phenotypic categorization of T cell malignancies.

Modulation of lymphocyte interaction with endothelium and homing by HIV-1 gp120.

We have previously shown that HIV-1 glycoprotein 120 (gp120) induces CD4 association with several molecules on the surface of CD4+ lymphocytes. Since one of these molecules was CD38, involved in lymphocyte/endothelium interaction, this article examines the possibility that gp120/CD4 binding alters CD4+ T cell interaction with vascular endothelium in vitro and in vivo. Cocapping experiments showed that gp120 induced CD4 association with CD38, CD29, CD49d, and CD11a in peripheral blood CD4+ T cells. Two in vitro binding assays were used to evaluate the effect of gp120. A static binding assay, performed at 37 degrees C, evaluated stable interactions mediated by integrins, and a dynamic binding assay, performed at 4 degrees C on a rocking shelf, evaluated weak interactions mediated by constitutively active molecules such as selectins and CD38. Gp120 increased dynamic binding and inhibited static binding to the endothelium of peripheral blood CD4+ T cells and SUPT-1 cells. Binding inhibition with mAbs suggested that the gp120 effect on dynamic binding involved CD38, CD31, and CD49d, whereas the effect on static binding involved CD11a and CD49d. In vivo experiments showed that treatment of 2D4 cells, a CD4- CD8- mouse T cell clone transfected with the human CD4, with gp120 increased their homing into the spleen, intestine, and mesenteric lymph nodes, whereas it decreased homing into peripheral lymph nodes. Alteration of lymphocyte homing may contribute to immune deficiency in HIV-1+ patients by decreasing the probability of an encounter between Ags and lymphocytes and inhibiting the spread of effector lymphocytes into tissues.

Deficiency of the Fas apoptosis pathway without Fas gene mutations in pediatric patients with autoimmunity/lymphoproliferation.

Fas (CD95) is a transmembrane molecule that induces programmed cell death (PCD) of lymphocytes. We examined its function in children with chronic thrombocytopenia, serum autoantibodies, and lymphadenopathy and/or splenomegaly. We found that T-cell lines from six of seven patients with this autoimmune/lymphoproliferative disease (ALD) were relatively resistant to PCD induced by monoclonal antibodies to Fas. By contrast, Fas function was normal in control patients with typical chronic idiopathic thrombocytopenic purpura (ITP) without lymphadenopathy. The defect was not due to decreased Fas expression, nor to over-production of soluble forms of Fas. Moreover, it specifically involved the Fas system because PCD was induced in the normal way by methylprednisolone. Complementary DNA sequencing of the Fas gene did not identify any causal mutation in patients with ALD. This distinguished them from patients with the human autoimmune lymphoproliferative syndrome (ALPS), who carry mutations of the Fas gene. Moreover, patients with ALD did not show the peripheral expansion of CD4/CD8 double-negative T cells that characterizes the ALPS phenotype. Fas signaling involves activation of a sphingomyelinase-catalyzing production of ceramide. We found that ceramide-induced PCD was defective in patients with ALD and not in patients with typical chronic ITP. These data suggest that the ALD patient defect involves the Fas signaling pathway downstream from the sphingomyelinase and that Fas gene mutations and double-negative T-cell expansion are not the only signs of a defective Fas system.

Characterization of H4: a mouse T lymphocyte activation molecule functionally associated with the CD3/T cell receptor.

The monoclonal antibody C398.4A was produced by immunizing Armenian hamsters with the mouse T cell clone D10.G4.1. It recognizes a molecule selectively expressed by activated mouse T cells and was named H4. H4 is expressed on the T cell surface about 24 h after activation and peaks at day 7. By contrast, it is not expressed by resting or activated B cells, macrophages, or fibroblasts. It is also expressed by CD4 or CD8 single-positive mature thymocytes. Immunoprecipitation showed that H4 is a disulfide-linked dimer, precipitating as a broad band at about 50-65 kDa under nonreducing conditions and at 25 and 29 kDa under reducing conditions. Deglycosylation of the reduced H4 by N-glycanase gave rise to a single band of about 21 kDa, suggesting that the two chains may be differentially glycosylated forms of the same protein. The H4 expression pattern and biochemical features, together with cross-blocking, co-capping, co-modulation, and immunoprecipitation preclearing experiments showed that H4 is different from other known co-stimulatory molecules such as CD69, CD2, Ly-6, CD25, OX-40, Mac-1 and LFA-1. By in vitro kinase assay, H4 was found to co-precipitate a tyrosine kinase activity that phosphorylated substrates of about 29 and 25 kDa. Co-modulation and co-capping experiments showed that H4 is physically associated with the CD3/T cell receptor. These data suggest that H4 may function as a T cell-specific co-stimulatory molecule and play a role in the T cell response when the activation stimulus is limited either because the antigen is only available in low concentration or has a low agonistic activity.

Modulation of CD4 lateral interaction with lymphocyte surface molecules induced by HIV-1 gp120.

CD4, a lymphocyte surface glycoprotein, serves as co-receptor for antigen with the T cell receptor (TCR). It is also the lymphocyte receptor for HIV by binding the gp120 viral envelope protein. Interaction of gp120 with CD4 is crucial for viral infection, but is not sufficient to allow viral entry into cells. Recombinant gp120 alters CD4+ T cell responsiveness to activation stimuli. To express its co-receptor function fully, CD4 must be laterally associated with the TCR and CD45 to form multi-receptor complexes competent to transduce potent activation signals. Here, we examine the possibility that gp120/CD4 binding alters lateral associations of CD4 with other lymphocyte surface molecules, and that assembly of abnormal multi-molecular complexes is involved in the gp120-induced CD4+ T cell dysfunction and in viral entry. In the absence of gp120, CD4 displayed high association with CD3, CD5, CD45RC, CD25, CD28, CD44, and CD53; weak association with CD2, CD38, CD45RB, CD62L, and CD26; and no association with CD45RA, CD45RO, CD11b, CD11a, CD54, CD7, CD48, CD98, CD59 CD55, HLA class I and class II molecules. Treatment with gp120 significantly increased CD4 association with CD3, CD45RA, CD45RB, CD59, CD38, CD26 and HLA class I, and decreased that with CD45RC. Specificity of these results were assessed at various levels. First, gp120 did not influence lateral associations displayed by other molecules, such as HLA class II. Second, the Leu3 mAb which binds CD4 on a site overlapping the gp120 binding site, did not elicit the same CD4 lateral associations as gp120, and finally, a direct gp120/CD4+ interaction was needed to induce the lateral associations, as shown by the observation that blocking the gp120/CD4 binding by the Leu3 mAb inhibited the gp120-induced associations. These results can be interpreted in several ways gp120/CD4 interaction could trigger an inside-out signal responsible for the associations, or gp120 could induce steric modifications of CD4 that increase its affinity for the associating molecules. Alternatively, these molecules may interact directly with gp120, bridging them with CD4. It is also possible that th e associations may be mediated by additional components, interacting with both gp120 and the associating surface molecule. The last hypothesis is likely for CD59, whose gp120-induced association with CD4 required the presence of serum in the co-capping assay. Since both CD59 and gp120 bind complement, the observed association could be mediated by complement components.

Interaction between endothelium and CD4+CD45RA+ lymphocytes. Role of the human CD38 molecule.

CD38 is a type II transmembrane glycoprotein, which is widely used as a marker for immature and activated lymphocytes, as well as plasma cells. Although its functional role and natural ligand are not known, CD38 has been shown to transduce activation signals to lymphocytes. Our work shows that CD38 is preferentially expressed by CD4+CD45RA+ cells, but not by CD4+CD45R0+ cells. CD4+CD45RA+ cells are reported to respond poorly to stimuli acting through the CD3/TCR in vitro and to display unique migration pathways in vivo. Cross-linking of CD38 by mAb did not overcome the hyporesponsiveness of CD4+ resting/naive cells to several activation stimuli; in contrast, CD38 engagement by mAb specifically inhibited their binding with human vein endothelial cells. These data suggest that CD38 may play a role in lymphocyte migration. The same inhibitory effect was detected on the (human x mouse) hybrid cell line CP410.A10, which expresses human CD38, but not on its CD38- subclone CP14. CD38 mAb did not inhibit the conventional binding assay between endothelium and several human CD38+ T and B cell lines. However, the inhibition was apparent when the binding assay was performed at 4 degrees C on a rocking shelf, conditions that minimized integrin function. These data suggest that CD38 mediates weak cell binding to endothelium, which is effective even in dynamic conditions. These features are reminiscent of those exerted by selectins, which are adhesion molecules that account for leukocyte rolling on vascular endothelial cells and play an important role in lymphocyte homing.

Expansion of T cells expressing low CD4 or CD8 levels in B-cell chronic lymphocytic leukemia: correlation with disease status and neoplastic phenotype.

Peripheral blood (PB) T cells from 56 patients with B-cell chronic lymphocytic leukemia (B-CLL) were analyzed by two- and three-color immunofluorescence (IF) to determine the expansion of distinct T-cell subsets and their relationship with the clinical and biological features of the disease. We detected the expansion of an unusual T-cell subpopulation expressing lower CD4 or CD8 levels (CD4lo, CD8lo) than classic T cells (CD4hi, CD8hi). This subpopulation also expressed low levels of the CD3/TCR alpha/beta complex and was CD19-CD13-CD14-. A phenotypic analysis probing the activation level of CD4lo, CD8lo, CD4hi, and CD8hi cells showed that they comprised increased counts of HLA-DR+, CD11b+, CD45R0+, and CD45RA+ cells. Subset expansion ranged from 2.1- to 13.6-fold. Statistical analysis showed that the size of some of these subsets was correlated to intrinsic features of the tumor. First, CD4loHLA-DR+ cell counts were higher in patients with stage A than those with stages B and C disease. Second, CD8loHLA-DR+ cell counts were higher in patients in stable remission than in those at diagnosis. Third, CD4loHLA-DR+, CD4loCD45R0+, CD4loCD45RA+, and CD4hiCD11b+ cell counts were higher in patients whose tumor cells expressed high levels of surface immunoglobulin (sIg) than in those expressing low levels. The involvement of CD4lo and CD8lo cells in most of these correlations suggests that they may be tumor-reactive cells. Similar cells described in human and murine autoimmune disease have been shown to be autoreactive anergic cells, which may derive from nonclassic pathways of T-cell development.

Co-stimulatory signal delivered by CD73 molecule to human CD45RAhiCD45ROlo (naive) CD8+ T lymphocytes.

CD73 is a molecule expressed by a subset of CD8+ human T lymphocytes and is involved in T cell activation. CD73 expression and function were analyzed in peripheral blood CD45RAhiCD45ROlo (naive) and CD45RAloCD45ROhi (memory) CD8+ cells. We found that CD73 was expressed by a majority of naive cells (74 +/- 12%), whereas fewer memory cells were CD73+ (29 +/- 10%). Moreover, CD73 was selectively expressed by the CD11b- subset of naive CD8+ cells, which were almost all CD73+. The same result was found on CD8+ cord blood lymphocytes, which prevalently display the naive phenotype. Naive CD8+ CD11b- cells were almost unresponsive to CD3 engagement, but this apparent anergy was completely overcome when CD3 and CD73 were simultaneously cross-linked by plastic-immobilized CD73 and CD3 mAb, showing that CD73 delivers an accessory signal that allows their activation via the CD3/TCR. This costimulatory signal was tenfold more potent than that induced by CD28 ligation. A phosphotyrosine analysis by Western blotting showed that cross-linking of CD73 induced the phosphorylation of two proteins with a molecular mass of approximately 28 and 100 kDa respectively, whereas ligation of CD3 induced phosphorylation of many substrates. When CD3 and CD73 were simultaneously triggered these substrates were hypophosphorylated. Because CD73 is linked to the cell surface by a GPI anchor, the transduction of this signal is probably mediated by a lateral interaction with transmembrane molecules. This hypothesis was assessed by cocapping, which showed that CD73 associates strongly with CD45RC, moderately with CD8, and weakly with CD3. These data suggest that CD73 signaling is coupled to both tyrosine kinase and phosphatase activities.

Isoform-specific associations of CD45 with accessory molecules in human T lymphocytes.

Association of CD45 with surface molecules was investigated in human T lymphocytes by co-capping. CD45 appeared to be associated with the CD3/T cell receptor complex and with CD4 or CD8 molecules in memory, but not in naive T cells, as previously reported in the mouse. Associations of CD45 isoforms with accessory molecules were then identified with seven anti-CD45R monoclonal antibodies (mAb). An isoform-specific association pattern was observed: CD2 co-capped with CD45 molecules recognized by UCHL1 mAb (CD45R0). LFA-1 with molecules bound by 2H4 mAb (CD45RA), and both CD4 and CD8 with molecules reacting with MCA.347 mAb (whose isoform specificity was not known). Further information on the CD45 isoform(s) associated to CD4 and CD8 was sought by assessing the isoform specificity of MCA.347. Cross-competition experiments showed that it reacts with an epitope clearly different from those recognized by 2H4 and UCHL1, and only partially overlapping the PD7/26 epitope (CD45RB). Moreover, the competition between MCA.347 and PD7/26 was maximal in naive T cells and minimal both in memory T cells and in a subset expressing CD11b, a marker of granular lymphocytes. Immunoprecipitation experiments showed that MCA.347 binds to CD45 molecules with a molecular mass of 220, 205 and 190 kDa, the 190-kDa molecules not being recognized by 2H4, PD7/26 or UCHL1. These data indicate that MCA.347 recognizes amino acid sequences different from those coded by the exon A or B of the gene, and not expressed by CD45R0, suggesting that it binds to sequences coded by the exon C. In conclusion, this work shows that in human T cells different CD45 isoforms are associated to different surface molecules: LFA-1 is associated to CD45RA, CD2 to CD45R0 and CD4 and CD8 presumably to CD45RC. This peculiar behavior of CD45 suggests that it may play a crucial role in lymphocyte activation, probably by modulating the signals delivered to the cell by different receptor systems.

Detection of hyperreactive T cells in multiple myeloma by multivalent cross-linking of the CD3/TCR complex.

Cellular immunity was investigated in 43 patients with multiple myeloma (MM) by assessing 3HTdR uptake induced by monocyte-dependent [CD3 monoclonal antibodies (MoAbs), phytohemagglutinin (PHA)] and monocyte-independent (CD2 MoAbs, ionomycin + phorbolester) stimulations. The former were evaluated in peripheral blood mononuclear cells (PBMNC) and purified T cells; the latter were evaluated in purified T-cell preparations only. MM showed significantly lower PBMNC responses to PHA (P less than .001), soluble OKT3 (CD3) (P = .01), and immobilized OKT3 MoAbs (P = .01). On purification of T cells, MM responses were still defective to soluble T11(2) + T11(3) (CD2) MoAbs (P = .004), phorbol myristate acetate (PMA) plus ionomycin (P less than .001), but significantly higher to plastic-immobilized OKT3 (P = .004). In some MM, 3HTdR uptake, interleukin-2 (IL-2) receptor (CD25) expression, and IL-2 production were as high on stimulation with plastic-immobilized OKT3 as that observed in normal subjects under optimal conditions (ie, plastic-immobilized OKT3 plus accessory signals). CD3 hyperreactivity correlated with the number of CD8+ HLA-DR+ cells in MM T-cell preparations. MM patients with more than 10% CD8+ HLA-DR+ cells had significantly higher responses to immobilized OKT3 (P less than .001), but lower responses to T11(2) plus T11(3) (P = .01), and PMA plus ionomycin (P = .03) than patients with less than 10% CD8+ HLA-DR+ cells. Phenotyping of CD45RA (naive) and CD45R0 (memory) expressions in resting MM T cells showed a lower ratio of CD45RA to CD45R0 in both CD4 (P less than .05) and CD8 (P less than .001) subpopulations. These data indicate that (a) some MM T cells require significantly fewer accessory signals (if any) to express the IL-2 receptor fully, secrete IL-2, and proliferate on multivalent cross-linking of the CD3/TCR complex; and (b) this peculiar state of activation is associated with high HLA-DR expression in CD8+ lymphocytes.

Multiple myeloma: increased circulating lymphocytes carrying plasma cell-associated antigens as an indicator of poor survival.

In multiple myeloma (MM) an increase in circulating lymphocytes expressing plasma cell-associated antigens (PCAA) has been described. Its prognostic significance was evaluated in this study. The immunologic phenotype of peripheral blood lymphocytes was analyzed with a panel of monoclonal antibodies specific for B, T, natural killer lymphocytes, and PCAA (CD38, PCA1) in 52 MM patients at diagnosis, remission, and during relapse, 18 monoclonal gammopathy of undetermined significance (MGUS), and 25 normal controls. No significant phenotypic alteration was observed in MGUS. In MM, the number of B lymphocytes was in the normal range at diagnosis and during the subsequent phases. A CD4/CD8 ratio decrease, during relapse, was due to both a CD4+ reduction and to an expansion of a subset of CD8+ activated suppressor lymphocytes. CD38+ and PCA1+ lymphocytes at diagnosis were significantly higher than in MGUS, and a further increase was observed during relapse, suggesting a correlation between PCAA expression and disease activity. The prognostic significance of increased PCAA was confirmed by a survival analysis of 32 patients evaluated at diagnosis using a CD38 cutoff of 0.45 x 10(9)/L positive lymphocytes. Median survival for patients with high values was only 14 months, whereas it was not reached at 32 months by those with low values (P less than .0007).

Multiple myeloma: altered CD4/CD8 ratio in bone marrow.

The expression of CD3, CD4 and CD8 antigens was simultaneously evaluated in peripheral blood and bone marrow lymphocytes from 22 multiple myeloma (MM) patients. The coexpression of CD11b and HLA-DR antigens was also analyzed within the CD4+ and CD8+ subpopulations in 4 MM patients. In peripheral blood the percentage of CD3+ and CD8+ cells was in the normal range, and the percentage of CD4+ was slightly reduced, leading to an altered CD4/CD8 ratio (less than 1) in only 7 patients. On the contrary, in bone marrow the percentage of CD4+ was profoundly reduced, leading to an altered CD4/CD8 ratio in all MM patients. As we previously reported in peripheral blood, an expansion of the CD11b+ and HLA-DR+ lymphocytes was observed within the CD4+ and CD8+ bone marrow T-cell subpopulations. A T-lymphocyte subset imbalance is more evident in bone marrow than in peripheral blood, and it is not due to a different lymphocyte distribution within the hematological compartments.

Monoclonal immunoglobulin gene rearrangement in peripheral lymphocytes of a patient with multiple myeloma.

We analyzed the immunoglobulin (Ig) heavy chain gene rearrangement in the peripheral blood lymphocytes of a patient with multiple myeloma (MM). Although the morphological and immunological examination did not reveal the presence of circulating plasma cells, a monoclonal Ig gene rearrangement was detected. This observation indicates that a monoclonal expansion of circulating B cells was present in the peripheral lymphocytes of this patient.

Multiple myeloma: beta-2-microglobulin is not a useful follow-up parameter.

Serum beta-2-microglobulin (beta 2M) has been suggested as the most powerful prognostic factor in multiple myeloma (MM). This paper investigates its ability to detect remission and relapse in individual patients. A correlation analysis was carried out between beta 2M and M component determinations, at diagnosis and monthly during follow-up in 21 consecutive MM patients with normal renal function. A statistically significant correlation was observed in 52.4% only. The lack of correlation in the remaining cases was due to low beta 2M production at diagnosis, or independent fluctuation of these 2 parameters. Serum beta 2M proved a much less reliable parameter for the detection of tumour variations than simpler M-component determination.

Early responder myeloma: kinetic studies identify a patient subgroup characterized by very poor prognosis.

In order to assess the prognostic value of rapid tumor mass reduction in responding multiple myeloma (MM) patients, 100 consecutive patients were analyzed, and bone marrow plasma cell kinetic characteristics were evaluated at diagnosis. Forty-two patients obtained a tumor mass reduction greater than or equal to 50% with three cycles of chemotherapy and within 3 months (early responder myeloma [ERM]), and 23 in greater than 3 months (slow responder myeloma [SRM]). Survival rates in these two groups were not statistically different (P = .07). The labeling index (LI) of bone marrow plasma cells was significantly higher in ERM patients than in SRM patients (1.8 +/- 2.0 v 0.8 +/- 0.7, P = .006). The LI was used to separate the ERM patients into two well-defined subgroups. ERM patients with a LI greater than or equal to 2% showed a median survival of 16.4 months, whereas ERM patients with a LI less than 2% did not reach the median survival at 46.9 months (P less than .0044). Remission duration was also significantly different: 12.2 months in the high LI subgroup and 26.3 months in the low LI subgroup (P less than .0025). Early response itself does not correspond to shorter remission duration and shorter survival, but it is a poor prognostic factor if associated with a high plasma cell proliferative activity.

Emergence of activated lymphocytes in CD4 and CD8 subpopulations of multiple myeloma: correlation with the expansion of suppressor T-cells (CD8+ OKM1+) and ecto-5'nucleotidase deficiency.

This study of CD4 and CD8 lymphocyte subpopulations in MM revealed increased proportions of cells expressing OKM1, Leu7, and HLA-DR antigens. In CD8 lymphocytes, there was a direct correlation between OKM1 and HLA-DR positivity. Two-colour analysis of purified CD8 subpopulations showed that HLA-DR was preferentially expressed by OKM1+ lymphocytes (suppressor cells), but a significant proportion of OKM1-lymphocytes (cytotoxic precursor cells) were also HLA-DR+. A significant proliferative activity found in CD2 lymphocytes was directly correlated with the proportion of HLA-DR+ cells in CD8 subpopulations only. CD8 lymphocytes displayed significantly lower 5'NT activity than those of normal subjects. This enzyme deficiency was correlated with the expansion of CD8 OKM1+ and HLA-DR+ cells; the increase in suppressor cells, as well as the emergence of activated cells, are associated with CD8 5'NT deficiency. In conclusion, the immunological pattern of CD4 and CD8 subpopulations in MM is significantly different from that in normal subjects. The implications of these data for the immune dysregulation occurring in MM are discussed.

Lack of correlation between plasma cell thymidine labelling index and serum beta-2-microglobulin in monoclonal gammopathies.

Simultaneous evaluation of bone marrow plasma cell thymidine labelling index (LI) and serum beta-2-microglobulin (SB2M) was performed in 146 patients with multiple myeloma (MM) or monoclonal gammopathy of undetermined significance (MGUS). Eighty patients had MM on diagnosis, 11 were in relapse and 12 were in remission phase; 43 patients had MGUS. All the evaluated patients had normal renal function with a creatinine level less than 1.4 mg%. Overall there was no direct correlation between LI% and SB2M. LI% best reflected the proliferative capacity of the tumor clone itself being less than or equal to 1% in MGUS and MM in remission, but greater than 2% at relapse of MM. SB2M correlated best with the stage of disease and tumor burden. These two factors therefore have different clinical utility: LI is a useful parameter to detect disease stability (e.g., MGUS) or highly proliferative disease (aggressive MM at diagnosis or early relapse). SB2M remains the best single predictor of patient tumor burden and associated survival duration.