Background: We evaluated a culture method for enumeration of residual T cells remaining in marrow after treatment with antibody and complement or with immunotoxin.
Methods: Marrow cells were cultured at limiting dilutions with phytohemagglutinin in the presence of Epstein Barr virus transformed human lymphoblastoid cells, and supernates were tested three days later for IL-2 by a cell proliferation assay. This method provides a simple, reliable, objective and rapid enumeration of T cells in marrow before and after treatment.
Results: Approximately 6% of untreated marrow mononuclear cells can produce IL-2 in such clonal cultures. Treatment with antibodies and complement under conditions identical to those used for our previous clinical trials produced a 3.7 log depletion of IL-2 precursors, whereas treatment with a ricin A chain anti-CD3 immunotoxin produced a 3.0 log depletion.
Conclusions: Clinical correlations are in progress for assessing whether T cell depletion evaluated with the present method equals previous techniques. The extreme depletion of T cells accomplished by these methods may partly account for the high graft failure rate seen in our clinical trials.