Idiotype Vaccination of Untreated Indolent B-Cell Lymphoma: Durable Objective Remissions and Association of Superior Outcome with Cellular Immune Responses

Idiotype vaccination refers to active immunization of B-cell lymphoma (B-NHL) patients with the clonal immunoglobulin (Ig) expressed by the tumor cells. After systemic cytoreductive therapy, idiotype vaccination has been shown to induce specific cellular and humoral immune responses; and humoral responses in particular are associated with prolonged remission and encouraging survival rates. Conventional idiotype vaccines are composed of the entire lymphoma-derived Ig coupled to the immunogenic carrier KLH and are administered subcutaneously with adjuvant. We have developed a idiotype production strategy based on bacterial expression of the lymphoma-derived idiotype as a recombinant Fab fragment (Bertinetti et al., EJH 2006). Intradermal administration of this antigen with lipid-based adjuvant and subcutaneous coadministration of GM-CSF had excellent immunogenicity in a phase I trial of advanced, heavily pretreated B-NHL patients (Bertinetti et al., Cancer Research 2006). In a subsequent phase II trial, 20 patients with untreated indolent B-NHL (14 follicular [FL], 3 nodal marginal zone [nMZL], 3 mantle cell [MCL]) and without immediate need for cytoreduction received at least 6 monthly idiotype vaccinations. No grade IV toxicities were seen, and the sole case of grade III toxicity, generalized erythema, did not preclude completion of the vaccination schedule. Prior to vaccination, 5/19 patients (26%) had decreased CD4⁺ and 6/19 patients (31%) low CD8⁺ T cells counts. Furthermore, 10/12 anti-HbS-negative patients (83%) failed to mount a detectable immune response to a conventional hepatitis B vaccine administered concomitantly to idiotype vaccination. Despite this functional immunodeficiency, 12/18 analyzed patients (66%) developed a cellular immune response to idiotype as detected by enumeration of IFNgamma-secreting cells by DC-ELISpot. The ELISpot protocol was validated by blinded interlaboratory testing (www.cimt.de). The frequency of idiotype-responding T cells increased from the 2nd to the 6th vaccination and could be effectively boostered by maintenance immunization in 3-monthly intervals. In vitro stimulation of PBMC from responding patients with idiotype induced specific proliferation of CD4⁺ T-cells and a shift towards a Th1 response in post-vaccination samples. In addition, 8/18 analyzed patients (44%) developed anti-idiotype IgG or IgM antibodies as assessed by ELISA, and the combined immune response rate was 85%. After a median follow-up of 34 months, 8 patients (40%) are progression-free, and 10 (50%) did not require cytoreductive therapy. Cellular immune responses were associated with superior PFS (p<0.05), and 5 of 6 non-responders eventually required cytoreductive therapy. Humoral immune responses were not related to PFS. Six patients (30%; only FL or nMZL) achieved an objective partial remission, including near-complete disappearance of a large submandibular mass and one subcutaneous lymphoma mass. All objective responders developed specific cellular immunity, but only 4 anti-idiotype antibodies. Five patients are in continuing remission for 12–49 months. Intradermal immunization with the chosen idiotype formulation has excellent immunogenicity despite a severely impaired immune function in untreated B-NHL patients. Furthermore, this is the first active immunotherapy trial showing objective and durable lymphoma responses in first-line therapy at a higher rate than expected for spontaneous remissions. In this setting, and in contrast to conventional idiotype vaccination schedules, cellular anti-idiotype immunity may play a crucial role for a favorable clinical outcome. Since passive humoral anti-lymphoma immunity can be easily transferred by infusions of commercially available monoclonal antibodies, synergistic benefit may be envisioned for an initial vaccination course aimed to prime anti-idiotype T-cells combined with subsequent passive immunotherapy.