Vaccine Response In Recipients of HLA Mismatched Unrelated Double Unit Cord Blood Transplantation (CBT).

Abstract 1247

The use of CBT has increased steadily over the last decade, with recent studies showing long-term progression-free survival similar to that of unrelated volunteer donor transplant recipients. The ability of CBT survivors to respond to post-transplant immunizations may differ from other allogeneic transplant populations due to the lack of transfer of memory T- and B-cells with the graft. Limited data have been reported on vaccine responses following this treatment modality. We, therefore, analyzed responses to immunizations in 23 double-unit CB recipients (17 adults, 6 children) transplanted at our center from 10/05-12/08. Patients were transplanted at a median age of 34 years (range 7–61) for the treatment of acute leukemia (n=13), or lymphoma/CLL (n=8/2). They received high-dose myeloablative (n=11), reduced intensity myeloablative (n=5), or non-myeloablative (n=7) conditioning according to diagnosis, age, prior therapy, and co-morbidities. GVHD prophylaxis consisted of a calcineurin inhibitor and mycophenolate mofetil. No patient received ATG. The study patients had sustained engraftment with a 5/6 (n=12) or 4/6 (n=11) HLA-matched unit. Seven recipients received rituximab (median 4 doses, range: 4–8) as planned post-transplant therapy for B-cell malignancies (n=6) or treatment of an autoimmune hemolytic anemia (n=1). Eleven patients had a history of grade II-IV acute GVHD and 5 had ongoing late acute or chronic GVHD prior to vaccination. Criteria for vaccination were: CD4 cell count of at least 200 cells/ul, PHA of greater than 60% lower limit of normal and serum IgG level >500 mg/dl at least 6 weeks following the last dose of IVIG. The median time to vaccination was 1.26 years post-CBT; this time was significantly longer in patients treated with Rituximab compared to those who were not (1.6 years versus 1.2 years, p=0.02), due to delayed normalization of B-cell numbers in the former group (449 days vs 108 days, p=0.004).Pre-vaccination titers obtained at a median of 1 year post-CBT demonstrated that over 85% of patients lacked protection against Pneumococcus, H. influenzae, and Pertussis, and at least 50% lacked immunity against tetanus, measles, and mumps. Seroconversion or >3- fold rise in titer was observed in response to tetanus, diphtheria, H. influenzae, and Pneumococcus in 90% (18/20), 81% (13/16), 80% (16/20)and 90% (18/20) of patients and was not significantly different in patients with or without a history of acute or chronic GVHD. Whereas 90% (5/6) of patients without a history of GVHD responded to a series of Hepatitis B immunizations, only 22% (2/9) of those with prior acute and/or chronic GVHD did so (p=0.03). No patient was protected against pertussis following a single TDaP (n=14) and only 1 of 5 patients responded to the protein conjugated meningococcal vaccine. Immunization with a live attenuated vaccine was initiated in 7 seronegative patients, including all 6 children, at a median of 2.25 years (range 1.5–3.6) post-CBT (MMR, n=7, Varivax, n=3). Seroconversion against measles, mumps, rubella, or chickenpox was observed in 3/7, 2/7, 6/7, and 1/3 patients, respectively. There were no serious reactions to any vaccine. These data suggest that CBT recipients are capable of responding to tetanus, diphtheria, H. Influenza and pneumococcal vaccines similar to other transplant groups. Nonetheless, the sub-optimal response to pathogens associated with outbreaks in the community (Hepatitis B, Pertussis, meningococcus, measles, mumps, varicella) highlight the need to obtain pre- and post-vaccination titers to document response, as well as define the optimal schedule of post-transplant immunizations specifically in this transplant population.