Treatment of Recurrent Refractory Pediatric Pre-B Acute Lymphoblastic Leukemia Using Inotuzumab Ozogamicin Monotherapy Resulting in CD22 Antigen Expression Loss as a Mechanism of Therapy Resistance.

BACKGROUND:Inotuzumab ozogamicin is a novel antibody-drug conjugate that targets CD22, a common antigen on pre-B acute lymphoblastic leukemia cells. OBSERVATIONS:A 7-year-old boy with pre-B acute lymphoblastic leukemia in his second relapse was given 2 cycles of inotuzumab ozogamicin. He responded morphologically with a negative bone marrow evaluation. However, he relapsed in cycle 3 of therapy with a loss of CD22 expression on his lymphoblast population. CONCLUSION:To our knowledge, this is the first published case of CD22 expression loss as a mechanism of therapy resistance for inotuzumab ozogamicin.