Both humoral and CTL-specific responses were induced by KLH-conjugated IGKV3-20 protein in HLA-A2-transgenic mice and coinjection of IGKV3-20-specific CTLs with IGKV3-20+ or IGKV3-15+ lymphoma cells into SCID mice totally prevented tumor growth, thus confirming the ability of these effectors to mediate efficient and cross-reactive cytotoxic responses also in vivo.