MULTICOLOR FLOW-CYTOMETRY ANALYSIS OF BLOOD-CELL SUBSETS IN PATIENTS GIVEN TOTAL-BODY IRRADIATION BEFORE BONE-MARROW TRANSPLANTATION

Purpose: Bone marrow transplantation has often been closely linked wit h accidental or intentional therapeutical irradiation. In both situati ons, study of the radiosensitivity of human blood cell subsets is of i nterest. Using one-color flow cytometry analysis of B lymphocytes, T c ell subsets, and natural killer cells, we previously reported that lym phocyte subsets exhibit equal radiosensitivity. Taking advantage of re cent developments in the knowledge of leukocyte differentiation antige ns and flow cytometry technology we undertook a study of blood cell su bsets to search for rare populations exhibiting different radiosensiti vity. Methods and Materials: Thirty patients, who were delivered a 12 Gy fractionated total body irradiation as part of their conditioning r egimen before transplantation for malignant disorders, were studied us ing multicolor how cytometry. Results: T and B lymphocytes showed a sh arp, radiation-induced decrease, with the B lymphocytes (cluster of di fferentiation (CD) 19+) being the most sensitive. When analyzed by mul ticolor flow cytometry, all major lymphocyte subsets appeared equally sensitive to the in vivo irradiation; that is, CD3+4+45RO+, CD3+4+45RA +, CD3+4+8-, CD3+4-8+. Therefore, all major lymphocyte subsets sharing the helper phenotype (naive or memory) and the cytotoxic phenotype ap peared equally sensitive to in vivo whole body irradiation. In paralle l, the CD34+ cell subset remained basically unchanged after whole body irradiation. Finally, the CD3-, 56+, 16+ natural killer cell subset w as relatively radioresistant (91 and 74% of its initial value, after 2 and 4 Gy, respectively) as compared to other lymphocyte subsets. Conc lusion: Our study provides evidence that T and B cell subsets seem to be highly radiosensitive in vivo. The CD34+ progenitor/stem cells and NK cells seem to be more radioresistant. This latter result might prov ide clues to the understanding of the pathophysiogeny of radiation-ind uced aplasia and of the engrafment/rejection process following bone ma rrow transplantation.