Abstract 4595: Moxetumomab pasudotox spares CD4 and CD8 lymphocytes in multiply relapsed hairy cell leukemia patients, while prospective trials of first, second, and later lines of purine analogs show increasing toxicity

The purine nucleoside analogs cladribine and pentostatin damage DNA and cause long-term suppression of CD4 and CD8 lymphocytes in patients with hairy cell leukemia (HCL). There is increasing concern that these reductions, particularly in CD4+ T-cells, may be associated with opportunistic infections and secondary malignancies. The anti-CD22 recombinant immunotoxin moxetumomab pasudotox targets HCL without damaging DNA, and spares T-cells. In a phase 1 trial, 20 patients treated with 50 ug/Kg every other day for 3 doses for 2-8 (median 4) cycles were evaluated for T-cell subsets. CD4 cells increased -56% to 152% (median 46%) after end of treatment, decreasing in only 1 of the 20 patients. Because there is very little prospective data on the effect of purine analogs on T-cells, we analyzed data from 80 consecutively enrolled patients receiving cladribine in first line, 40 receiving cladribine in second line, and 52 receiving either pentostatin or bendamustine in third or later lines. The latter group was most appropriate to compare with moxetumomab pasudotox, which was also used in third or later-line treatment of HCL. CD4 counts after moxetumomab pasudotox were 85-600 (median 424), compared to 22-618 (median 73) after third or later line purine analog (p