Rapid early monoclonal protein reduction after therapy with bortezomib or bortezomib and pegylated liposomal doxorubicin in relapsed/refractory myeloma is associated with a longer time to progression.

BACKGROUND: A rapid and early monoclonal (M) protein response during initial therapy in patients with multiple myeloma had been identified as a predictor of superior long-term outcome in some--but not all--studies. METHODS: To determine if the parameter of M protein reduction was of value in the relapsed and/or refractory setting, retrospective landmark analyses were performed at the end of cycles 2 and 4 of a phase 3 study, which randomized such patients to receive bortezomib alone or pegylated liposomal doxorubicin (PLD) with bortezomib. RESULTS: Compared with a <25% reduction in M protein at the landmark time point, patients with a 50% to <75% reduction after cycle 2 had a significantly lower hazard ratio (HR) for time to progression (HR = 0.41; 95% confidence interval [CI], 0.26-0.64; P <.001), as did those with a ≥75% reduction (HR = 0.26; 95% CI, 0.15-0.45; P < .001). In all of these groups, PLD + bortezomib provided superior outcomes to bortezomib alone, and did so without an increase in the risk of adverse events overall and with a predictable toxicity profile. CONCLUSIONS: These analyses supported the possibility that a robust early M protein response is a good prognostic factor for long-term outcome of myeloma patients with relapsed and/or refractory disease receiving bortezomib or PLD + bortezomib.

The mechanism of intestinal uptake and transcellular transport of IgG in the neonatal rat.

The transport of immunoglobulins across the intestinal mucosa of neonatal rats provides an excellent model for the study of transcellular protein transport. The mechanism of intestinal uptake and transcellular transport of plasma proteins has been studied in 12-14-day old rats using intraduodenally administered radioiodinated proteins. Appreciable quantities of rat IgG, mouse IgG, rabbit IgG, and all four subclasses of human IgG were taken up by the intestinal wall (19-54% of administered dose at 4 hr) and transported to the animal (10-35% of administered dose at 4 hr). In contrast there was little or no uptake of human IgM, IgA, and IgE and little or no transport of human IgM, IgA, IgD, IgE, albumin, transferrin, and ceruloplasmin. Both the uptake and transport of labeled IgG were significantly inhibited by unlabeled IgG. Further insight into the transport process was obtained from the observation that an appreciable proportion of the label of IgG in intestinal wall homogenates, but not in plasma or intestinal washings, migrated in a sucrose ultracentrifugation gradient much more rapidly than did the administered 7S molecules. This pattern was not observed with other proteins studied. This apparent binding of labeled IgG was also markedly inhibited by unlabeled IgG. In subcellular fractionation studies of intestinal homogenates the complexed labeled IgG was shown to be associated predominantly with cell membrane rather than cell sap fractions. In addition IgG could be shown to bind to purified enterocyte microvillous membranes in vitro. IT IS CONCLUDED THAT IN THE NEONATAL RAT: (a) the major processes involved in both intestinal uptake and transport of IgG are specific and saturable; (b) intestinal transport is associated with complexing of IgG molecules with membranes, most probably with enterocyte microvillous membranes; and (c) the part of the IgG structure involved in this process is probably similar to that involved in the concentration-catabolism effect but is not identical to that mediating other non-antigen combining functions of IgG. Our data are consistent with the existence of specific receptors for IgG on enterocyte microvillous membranes of the neonatal rat. Such receptors would be necessary for the specific uptake and transport of these molecules.

Inhibition or acceleration of fibrin polymerization by monoclonal immunoglobulins and immunoglobulin fragments.

A prolongation of the thrombin clotting time by at least 25% was found in the presence of 8 of 26 IgG myeloma proteins, 2 of 5 IgA proteins and 1 of 10 macroglobulins, in a concentration of 10 mg/ml. Normal pooled immunoglobulin in concentrations up to 83 mg/ml were inactive. 2 IgG and 2 IgM monoclonal immunoglobulins caused an acceleration of the thrombin time by at least 20%; this phenomenon has not been reported before. Corresponding results were obtained with these proteins when the polymerization of des-AA and des-AABB fibrin monomers were investigated in a light scattering system. Studies with enzymatically produced Fab, F(ab')2 and Fc fragments from normal and monoclonal immunoglobulin suggested that the polymerization inhibitory activity resides in the Fab portion of the immunoglobulin molecule. While the ability to inhibit fibrin polymerization may be an immunoglobulin specific effect, the acceleration caused by certain other monoclonal immunoglobulins may be an unspecific effect similar to that seen with dextran or albumin.

Superior overall survival of patients with myeloma achieving very good partial response or better to initial treatment with bortezomib, pegylated liposomal doxorubicin, and dexamethasone, predicted after two cycles by a free light chain- and M-protein-based model: extended follow-up of a phase II trial.

In myeloma, achievement of very good partial response (VGPR) post-transplant is associated with prolonged overall (OS) and progression-free survival (PFS). In this study of bortezomib, pegylated liposomal doxorubicin, and dexamethasone (VDD) in 40 patients with newly diagnosed myeloma (median follow-up 45.1 months), 2-/4-year OS estimates were 95.7%/86.5% versus 82.4%/58.2% for patients achieving ≥VGPR versus 

Membrane immunoglobulins of spontaneous B lymphomas of aged BALB/c mice.

Four cell lines derived from spontaneous BALB/c lymphoma tumors were analyzed with regard to the type of their membrane immunoglobulins (Ig). Using lactoperoxidase iodination of membrane proteins combined with immunoprecipitation and electrophoresis on polyacrylamide gel, three of these cell lines (X16c, L10A and K46) were found to express the monomeric form of IgM and IgD as well as half molecules. One cell line (M12) lacked both IgM and IgD. The apparent mol. wt of the lymphoma micro chain was about 80 000 and exceeded the mol. wt. of 75 000 determined for micro chains secreted by myeloma cells. The mol. wt. of the delta heavy chain was found to be 66 000. Immunofluorescence showed that the L10A and X16c lines expressed lambda light chains on their cell surface. Another Ig-bearing cell line (K46) expressed both lambda and kappa chains. Thus, three out of the four B lymphomas examined expressed both IgM and IgD with light chains of the Lambda type. These results, together with our previous findings which demonstrate the presence of Ia and Fc receptors on the same cells, indicate that spontaneous B lymphomas in BALB/c mice are the malignant counterpart of mature B lymphocytes.

Identification of a unique receptor on a group A streptococcus for the Fc region of human IgG3.

Receptors that bind to the Fc region of all four human IgG subclasses have been described on a number of strains of group A streptococci. In this study, we have demonstrated that these immunoglobulin binding properties are mediated by two distinct Fc receptors. The first receptor, with a Mr of approximately 56,000, binds to human IgG1, IgG2, and IgG4, but not to IgG3. A second receptor, with a Mr of approximately 38,000, binds exclusively to human immunoglobulins of the IgG3 subclass.

Evaluation of human oral organisms and pathogenic Streptococcus for production of IgA protease.

IgA protease is a proteolytic enzyme found in whole human saliva and in dental plaque that cleaves both secretory and myeloma IgA of human origin to yield intact Fabalpha and Fcalpha fragments. To determine which bacteria are capable of producing this enzyme, we have examined a variety of strains normally found in the human oral cavity and a number of streptococci of known Lancefield group serotype. Streptococci of groups A, B, C, D, F, G, H, M, and N, Streptococcus mutans, Streptococcus sanguis, Streptococcus mitior, Streptococcus salivarius, Streptococcus faecalis, Veillonella, Lactobacillus, Actinomyces, Propionibacterium, Bacteroides, and Fusobacterium were grown in liquid medium, and fluids were examined for IgA protease activity. Only S. sanguis and clinically isolated group H streptococci elaborated IgA protease under the culture conditions used. Negative strains could not be stimulated to produce the enzyme when cultured in the presence of secretory IgA. Among the natural oral bacteria, capacity to produce IgA protease is restricted to certain species of Streptococcus, notably those of the group H serotype. Since secretory immunity is mediated by the IgA class of antibody, the presence of this enzyme at mucosal surfaces could modify the secretory immune function.