Abstract An increasing set of B-cell non-Hodgkin’s lymphomas (B-NHLs) show a biased usage of IGKV3-20 and IGKV3-15 immunoglobulin genes, but it is not known whether the corresponding proteins are immunogenic in the majority of patients. We herein demonstrate that IGK+ lymphoma patients show spontaneous T cell responses to these proteins and that IGKV3-specific cytotoxic T lymphocytes (CTLs) can be easily induced ex vivo. IGKV3-20-specific CTLs cross-react against different IGKV3 proteins, an effect mediated by the presence of 21 shared, sometimes promiscuous, T cell epitopes, presented by the most common HLA class I allele products, thus assuring a broad HLA coverage of IGKV3-based vaccines. Many natural variants of these epitopes are carried by IGK light chains expressed by a broad spectrum of B-NHLs and we show that IGKV3-20-specific CTLs cross-react also against several of these variant epitopes. Both humoral and CTL specific responses were induced by KLH-conjugated IGKV3-20 protein in HLA-A2-transgenic mice and co-injection of IGKV3-20-specific CTLs with IGKV3-20+ lymphoma cells into SCID mice totally prevented tumor growth, thus confirming the ability of these effectors to mediate efficient cytotoxic responses also in vivo. These results provide the rationale to exploit IGKV3 proteins as “off-the-shelf” vaccines for a large fraction of lymphoma patients.