Rituximab is an effective treatment in patients with pemphigus vulgaris and demonstrates a steroid-sparing effect

BACKGROUND

Corticosteroids (CS) with or without adjuvant immunosuppressant agents are standard treatment for pemphigus vulgaris (PV). The efficacy of adjuvant therapies in minimizing steroid-related adverse events (AEs) is unproven.

OBJECTIVES

To utilize data collected in a French investigator-initiated, phase III, open-label, randomized controlled trial to demonstrate the efficacy and safety of rituximab and seek approval for its use in PV.

METHODS

This was an independently conducted post hoc analysis of the moderate-to-severe PV subset enrolled in the Ritux 3 study. Patients were randomized to rituximab plus 0·5 or 1·0 mg kg-1 per day prednisone tapered over 3 or 6 months, or 1·0 or 1·5 mg kg-1 per day prednisone alone tapered over 12 or 18 months, respectively (according to disease severity). The primary end point was complete remission at month 24 without CS (CRoff) for ≥ 2 months, and 24-month efficacy and safety results were also reported.

RESULTS

At month 24, 34 of 38 patients (90%) on rituximab plus prednisone achieved CRoff ≥ 2 months vs. 10 of 36 patients (28%) on prednisone alone. Median total cumulative prednisone dose was 5800 mg in the rituximab plus prednisone arm vs. 20 520 mg for prednisone alone. Eight of 36 patients (22%) who received prednisone alone withdrew from treatment owing to AEs; one rituximab-plus-prednisone patient withdrew due to pregnancy. Overall, 24 of 36 patients (67%) on prednisone alone experienced a grade 3/4 CS-related AE vs. 13 of 38 patients (34%) on rituximab plus prednisone.

CONCLUSIONS

In patients with moderate-to-severe PV, rituximab plus short-term prednisone was more effective than prednisone alone. Patients treated with rituximab had less CS exposure and were less likely to experience severe or life-threatening CS-related AEs. What's already known about this topic? Pemphigus vulgaris (PV) is the most common type of pemphigus. Corticosteroids, a standard first-line treatment for PV, have significant side-effects. Although their effects are unproven, adjuvant corticosteroid-sparing agents are routinely used to minimize steroid exposure and corticosteroid-related side-effects. There is evidence that the anti-CD20 antibody rituximab is effective in the treatment of patients with severe recalcitrant pemphigus and in patients with newly diagnosed pemphigus. What does this study add? This study provides a more detailed analysis of patients with PV enrolled in an investigator-initiated trial. Rituximab plus prednisone had a steroid-sparing effect and more patients achieved complete remission off prednisone. Fewer patients experienced grade 3 or grade 4 steroid-related adverse events than those on prednisone alone. This collaboration between academia and industry, utilizing independent post hoc analyses, led to regulatory authority approvals of rituximab in moderate-to-severe PV.

A role for CaMKII in T cell memory

In order to study the role of calcium/calmodulin kinase II (CaMKII) in T cells, we generated transgenic mice expressing CaMKIIgammaB* (T287D), a partially calcium-independent mutant of CaMKIIgammaB. In these mice, the size of the thymus was increased 1.5- to 2-fold, at least in part due to an increase in the lifespan of double-positive (DP) thymocytes. More importantly, there was an increase in the number of T cells in the secondary lymphoid organs that had acquired an antigen-dependent memory phenotype. These T cells were bonafide memory cells as assessed by a variety of criteria. In addition, T cells from wild-type mice acquired calcium-independent CaMKII activity after several rounds of antigen-stimulated division. We propose that CaMKII controls a distinct process of activation-induced cellular differentiation.

Antitumor vaccination using a major histocompatibility complex (MHC) class I-restricted pseudopeptide with reduced peptide bond

Synthetic peptides have raised a considerable interest in the fields of vaccines and immunotherapy. The authors previously introduced modifications into the peptide backbone of the H-2Kd-restricted epitope CW3. One of these pseudopeptides, C7, bound to Kd with an affinity identical to the parent peptide and was recognized by T cells specific for the parent peptide. The authors now show that this analog has an increased resistance to trypsin and displays an extended half-life in serum. The authors further tested its immunogenicity both in vitro and in vivo and found that cytotoxic T lymphocytes (CTL) induced against the peptide analog recognize the parent peptide. Moreover, analysis of T-cell receptor rearrangements by Immunoscope software revealed that C7-induced CTL display the hallmarks of the response against the parental epitope CW3. Administration of the pseudopeptide into DBA/2 mice induces a protective immune response against a lethal challenge with tumor cells expressing the parent peptide. Therefore, modifications in the backbone of antigenic peptides can decrease protease susceptibility while preserving immunogenicity. Such peptide analogues may therefore prove useful for the development of new therapeutic tools aimed at eradicating pathogens or tumors.

Tolerance to maternal immunoglobulins: resilience of the specific T cell repertoire in spite of long-lasting perturbations

T cell tolerance is established and maintained through various mechanisms, the critical component being the persistence of the specific Ag. However, at the molecular level, the nature of the recovering TCR repertoire following breakdown of tolerance is unknown. We address this important question by following kappa light chain constant region (C kappa)-specific CD4+ T cells of kappa light chain knock-out (kappa-/-) mice born to kappa+/- mothers. These cells, which were in contact with maternal kappa+ Igs from early ontogeny until weaning, were strongly tolerized. Tolerance was reversible and waned with the disappearance of peptide C kappa 134-148 presentation in lymphoid organs, including the thymus. Whereas three specific V beta-J beta rearrangements emerged in the peptide C kappa 134-148-specific CD4+ T cell response of all regular kappa-/- mice, soon after breakdown of tolerance only one of these rearrangements was detected. The two others displayed a significant delay in reappearance and were still rare at 26 wk of age, while the control proliferative response had already recovered 3 mo earlier. At 52 wk of age, a complete recovery of the three canonical V beta-J beta rearrangements was observed. Thus, although profoundly perturbed for several months, the T cell repertoire returns to equilibrium, highlighting the resilient nature of this system.

Role of peptide backbone in T cell recognition

T cells recognize self and nonself peptides presented by molecules of the MHC. Amino acid substitutions in the antigenic peptide showed that T cell specificity is highly degenerate. Recently, determination of the crystal structure of several TCR/MHC-peptide complexes suggested that the peptide backbone may significantly contribute to the interaction with the TCR. To directly investigate the role of the peptide backbone in T cell recognition, we performed a methylene-amino scan on the backbone of an antigenic peptide and measured the capacity of such pseudopeptides to bind their cognate MHC molecule, to sensitize target cells for T cell lysis, and to stimulate IL-2 secretion by two T cell hybridomas. For one of these pseudopeptides, we prepared fluorescent tetramers of MHC molecules and compared the staining of two T cell hybridomas. Our results demonstrate that the peptide backbone has an important contribution to TCR binding and suggest that some interactions between the peptide backbone and the TCR may be partially conserved. We discuss this finding in the perspective of TCR plasticity and T cell function.

Immunological issues in vaccine trials: T-cell responses

T-cell responses are both extremely diverse and dependent on the MHC of the immunized (or infected) individual. Apart from T-cell proliferation assays, the most informative functional T-cell assays are still difficult to perform. Antibody measurements provide a very indirect assessment of the helper arm of the T-cell response. On the other hand, measuring cytolytic T cells (CTL) remains a difficult task, which has precluded the evaluation of CTL responses in vaccine efficacy trials. Accordingly, even though there are reasons to suspect that CTL are important to clear certain infections and to vaccinate against certain diseases, particularly chronic viral infections such as that caused infection by HIV, the data to support these claims are largely missing in humans. Improving and automating CTL assays would have a significant impact on vaccine design. The Immunoscope technology is a PCR based approach which describes the T cell repertoire by several thousands of measurements. This allows the detection of clonal expansions and to evaluate the oligoclonality of pathological T cell infiltrates in humans. In the mouse, it has allowed us to establish the concept of public T-cell responses which are recurrent in individual animals sharing the same MHC. This concept can occasionally apply to humans since we found a public T-cell expansion in DR2a patients at the onset of multiple sclerosis. Single chain class I MHC molecules have been produced, purified, homogeneously loaded with an antigenic peptide, and coated on to beads. This formulation appears to be efficient for induction of primary CTL in vitro . A similar approach can be used to purify peptide specific T cells, and its coupling with the Immunoscope technology is being considered. The potential of these new approaches for T-cell analyses will be discussed.

Role of co-stimulation in CD8+ T cell activation

The two-signal model states that activation of naive T cells requires a signal 1 stimulus through the TCR and a co-stimulatory signal 2. By contrast, signal 1 alone is sufficient for pre-activated T cells. Recently, however, it has been shown that under certain conditions T cells can bypass the requirement for co-stimulation. For example, CD28-deficient mice, when immunized with lymphocytic choriomeningitis virus, mount a vigorous cytotoxic T lymphocyte response and clear the virus. As a continuous effort to unravel the mechanisms of T cell activation, we previously reported activation of hybridoma T cells by recombinant single-chain MHC molecules in the absence of antigen-presenting cells. In such reconstitution experiments, since the signals delivered to the T cells are well controlled, the contribution of any known or unknown signals can be ruled out. In the present study, we analyzed the requirements for activation of naive T cells by using splenocytes from TCR transgenic mice as a source of responding cells. We observed that naive CD8+ T cells are fully activated by signal 1 alone, but that co-stimulation lowers their activation threshold. Previously activated T cells are fully responsive, even when the first stimulation was performed in the absence of co-stimulation. They display a low activation threshold and are insensitive to co-stimulation. The physiological relevance of this finding and its consequences for immunotherapy as well as for our understanding of self-tolerance are discussed.

Efficient binding of reduced peptide bond pseudopeptides to major histocompatibility complex class I molecule

Reduced peptide bond pseudopeptide analogues have been examined for their ability to bind murine class I molecules of the major histocompatibility complex (MHC). Eight pseudopeptide analogues of an antigenic peptide derived from Plasmodium berghei (H-Ser252-Tyr-Ile-Pro-Ser-Ala-Glu-Lys-Ile260-OH) were obtained by systematically replacing one peptide bond at a time by a reduced peptide bond psi (CH2-NH). The resulting analogues were then tested for their binding to a recombinant single chain SC-Kd class I molecule. The comparative results show that five analogues can efficiently mimic the parent peptide while the introduction of the reduced bond between P3-P4, P7-P8, and P8-P9 is deleterious for SC-Kd binding. The fact that more stable pseudopeptides containing reduced peptide bonds can bind major histocompatibility complex molecules is of great interest for the design of peptidomimetics with potential therapeutical properties. Such peptide analogues may prove useful for the development of peptide-based cytotoxic T lymphocyte vaccines.