Higher Infused Lymphocyte Counts Improve Antibody Response to Immunization After Autologous Stem Cell Transplantation

Infectious diseases remain a leading cause of morbidity and mortality in patients who receive high-dose chemotherapy followed by Autologous Peripheral Blood Stem Cell Transplantation (APBSCT). Infectious disease complications of transplantation might be reduced by effective post-transplant immunization but reconstitution of the immune system may take months to years after transplantation and responses to immunization are often attenuated in this setting. Correlates of improved immune reconstitution and response to immunization after transplantation would be important to identify. It has been recently shown that higher absolute lymphocyte count in the infused stem cell autograft (A-ALC) and higher ALC at day +15 after stem cell infusion (ALC-15) are independently associated with improved overall survival after APBSCT. The mechanism of this association is unclear, but this finding suggests that improved immune responses to immunization might also be achieved with this approach making it possible to immunize at 6 months instead of at one year. This hypothesis has never been evaluated. Survival following APBSCT is improved with a higher A-ALC and ALC-15. It is postulated that the higher lymphocyte numbers correlate with improved immune surveillance and destruction of minimal residual disease. Thus, one must consider the probability higher A-ALC will confer improved response to T-cell dependent immunization early after transplant.