Differential Immunogenicity of Two Peptides Isolated by High Molecular Weight-Melanoma-Associated Antigen-Specific Monoclonal Antibodies with Different Affinities

Self Cite

The human high m.w.-melanoma-associated Ag (HMW-MAA) is an attractive target for the immunotherapy of melanoma, due to its relatively high expression in a high percentage of melanoma lesions and its restricted distribution in normal tissues. Active immunization with HMW-MAA mimics has been previously shown to induce a HMW-MAA-specific, T cell-dependent Ab response associated with an apparent clinically beneficial effect in advanced melanoma patients. Although T cells play an important role in controlling tumor growth, only limited information is available to date about the induction of HMW-MAA-specific CTL. In this report, we show that immunization of HLA-A2/Kb transgenic mice with HMW-MAA cDNA-transfected syngeneic dendritic cells elicited a CD8+ CTL response specific for HMW-MAA peptides with HLA-A2 Ag-binding motifs. The elicited CTL lysed HLA-A2+HMW-MAA+ melanoma cells in vitro, and mouse HLA-A2/Kb cells pulsed with HMW-MAA-derived peptides in vitro and in vivo. Although this CTL response could be generated in the absence of CD4+ T cell help, harnessing CD4+ T cell help in a noncognate Ag-specific manner with the polyclonal activator staphylococcal enterotoxin A augmented the CTL response. These results imply that dendritic cell-based immunization, in combination with CD4+ T cell help, represents an effective strategy to implement T cell-based immunotherapy targeting HMW-MAA in patients with HMW-MAA-bearing tumors.

Section: Sea a Polyclonal Cd4supporting

confidence: 80%

CD4-Dependent Potentiation of a High Molecular Weight-Melanoma-Associated Antigen-Specific CTL Response Elicited in HLA-A2/Kb Transgenic Mice

Peng

Luo

et al. 2006

Self Cite

“…This variability of the immune response is surprising because the animals have the same genetic background (they are inbred and from the same colony). Nonetheless, it was expected based on our previous work (13,19) and on similar observations with mimics of HLA (37) and other tumorassociated Ags (21,38). The mechanism underlying these findings has not been elucidated.…”

Section: Discussionmentioning

confidence: 95%

“…The finding that Rp5-L is an effective mimotope of CD20 in the absence of primary sequence homology is not without precedent (13,20,21). In such cases, the peptide mimotope mimics a conformational or discontinuous epitope.…”

Section: Discussionmentioning

confidence: 99%

Two Structurally Different Rituximab-Specific CD20 Mimotope Peptides Reveal That Rituximab Recognizes Two Different CD20-Associated Epitopes

Perosa

Favoino

Vicenti

et al. 2009

Peptide mimotopes of the CD20 epitope recognized by rituximab are useful tools for studying this therapeutic mAb’s functional properties. We previously identified two structurally different peptides that are both effective mimotopes: a 7-mer cyclic peptide (Rp15-C) bearing the antigenic motif a/sNPS that matches 170ANPS173 of the extracellular loop of CD20, and a 12-mer linear peptide (Rp5-L) containing the antigenic motif WPxWLE lacking sequence homology to CD20. In this study, we investigated whether the different structures of Rp15-C and Rp5-L reflect the mimicry of the same or different CD20 epitopes recognized by rituximab. Using immunochemical methods, we found that, like Rp15-C, Rp5-L mimics the raft-associated form of CD20 (by inhibiting rituximab binding to CD20 in vitro). Rp5-L and Rp15-C elicit, in immunized mice, anti-CD20 Abs that stain CD20+ cells with a punctate pattern similar to that of rituximab. However, only anti-Rp5-L Abs recognize denatured CD20. When phage-display peptide libraries were panned with anti-Rp5-L, phage clones were enriched that expressed the consensus qWPxwL, similar to the antigenic motif WPxWLE, but not matching a/sNPS. Finally, WPxWLE and ANPS share some, but not all, contact sites within the rituximab Ag-combining site, indicating that WPxWLE is not an exact replica of Rp15-C (or CD20) ANPS. Altogether, these results indicate that the two structurally different peptides are also conformationally different, and suggest that rituximab recognizes two different CD20-associated epitopes.

“…Mimotopes have been successfully isolated and shown to elicit Abs against the nominal Ags and/or to trigger biological effects similar to those of the PIT in different clinical settings, namely tumors (5)(6)(7)(8), autoimmune diseases (8,9), and infectious diseases (10,11).…”

Section: T He Cd4mentioning

confidence: 99%

Identification of an Antigenic and Immunogenic Motif Expressed by Two 7-Mer Rituximab-Specific Cyclic Peptide Mimotopes: Implication for Peptide-Based Active Immunotherapy

Perosa

Favoino

Vicenti

et al. 2007

Two 7-mer cyclic peptides—Rp15-C and Rp13-C—which bear the antigenic motif recognized by the anti-CD20 mAb rituximab, but have different motif-surrounding amino acids, show a comparable avidity for rituximab and inhibit the binding of rituximab to raft-associated CD20 and rituximab-induced membrane ceramide on human lymphoid Daudi cells. Their immunogenic profiles differed: Abs recognizing CD20 were induced in two and five of five BALB/c mice immunized with Rp15-C and Rp13-C, respectively. Analysis of immunogenic motif, performed by panning a 7-mer phage-display peptide library with purified anti-peptide IgGs, showed that the motif defined by anti-Rp15-C mostly included amino acids surrounding the rituximab-specific antigenic motif <aNPS>, whereas that defined by anti-Rp13-C was <NPS>. These data indicate that their motif-surrounding amino acids can markedly influence the specificity of Abs, even when elicited with a short 7-mer peptide. Because these anti-peptide Abs are of IgG isotype, their specificity is likely to reflect how peptides are processed at the T cell level and suggest that, within a short peptide, the motifs defined by T cells during the initial phase and upon their stimulation may be different. Our findings may account for the failure of most forms of peptide-based immunotherapy in cancer and autoimmune diseases in which anti-mimotope Abs are expected to play a relevant therapeutic effect. They also suggest strategies to implement the specificity of peptide-induced Abs against the target Ag.