Peptide-Vaccine Treatment Associated with TKI Therapy in Patients with CML Is Able to Induce Immunologic, Cytogenetic and Molecular Responses: a Single Center Experience with Long-Term Follow up.

The main objective in the intent to “cure” chronic myeloid leukemia (CML) is to obtain complete cytogenetic remission (CCR) and molecular remission. Tyrosin kinase inhibitors (TKI) treated patients (pts) achieve CCR, but BCR-ABL transcripts can still be detectable, and complete molecular remission (CMR), intended as undetectable transcript, are rare. Moreover about 10% of up-front treated patients show resistance to Imatinib, that reaches 30% in late chronic phase, loss of response during treatment is not negligible, and treatment cannot be stopped. Thus the eradication of residual disease still appears a difficult goal for a TKI alone. An alternative approach to target the residual disease is an active specific immunotherapy. We associated TKI therapy and immunogenic peptides derived from the p210 b3a2 and b2a2 fusion protein (developed by M. Bocchia et al. University of Siena) in pts with chronic phase (CP) CML with stable disease in trying to obtain a specific immunologic activation able to induce a measurable clinical response.

17 pts (11 M:6 F) with CP CML, median age 55,5 (range 30-68) treated with Imatinib (16) or Dasatinib (1) were enrolled in the studies. All patients but one were in late chronic phase and had been treated with 2 (2 pts), 3 (11 pts) or >3 (4 pts) lines of therapies. Median time from diagnosis was 64.1(16-143) months, and patients were treated for a median of 30.8 months with TKI before peptide vaccination. 15 pts had b3a2 and 2 a b2a2 transcript. Pts presented with stable, measurable disease at cytogenetic or molecular level from at last 6 months. Vaccination included GM-CSF pre treatment and administration of 5 p210 b3a2 (CMLVAX100) or 1 b2a2 (CMLVAX25) derived peptides. Treatment plan consisted of an induction plan of 6 vaccinations every two weeks, followed by additional boosts every 3-6 months for responding patients. During vaccination, patients continued their conventional treatment with Imatinib/Dasatinib. Prior to vaccine all patients were tested with an intradermal injection of peptides (DTH) to evaluate their sensitivity to the CML antigens, and all of them resulted negative. Cytogenetics, FISH and molecular biology, peptide-specific immune responses (DTH, CD4+ proliferation, immunophenotype) were analyzed before and during treatment.

15/17 pts are evaluable (2 patients had just completed the first 3 months and were not considered for their short follow up), and all patients but one showed a variable degree of response. All patients presented with some degree of DTH indicating the “recognition” of peptides by effector T cells (biologic response). 5/9 pts with positive cytogenetic (2-66% Ph+) reached CCR, and 3 also CMR, while 1 patient did not respond (the one with high tumor burden, 66% Ph+). 3/6 pts in CCR at time of vaccination reached CMR. The majority of responses were rapidly reached (after the induction) and were long lasting. After 69 month follow up 6/15 patients are still treated. Patients suspended vaccination due to: no response (1), lost CCR (5), progression (1), 2^nd neoplasm (1), allergic reaction (1). One patient that reached CCR and MCR after vaccination stopped imatinib and was closely monitored thereafter. She is now treated with only vaccine boosts twice/year and still in CMR after 28 month. Specific immune response will be described.

These data suggest that addition of b3a2 or b2a2-specific vaccine may have synergistc effect with TKI favouring reduction of residual disease and increasing the number of patients that reach CMR. A multicentric trial is ongoing through the GIMEMA CML study group, and a pilot study to stop TKI in long lasting CMR is in preparation.

No relevant conflicts of interest to declare.