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Screening for Deficits in DNA Repair by the Response of Irradiated Human Lymphocytes to Phytohemagglutinin¹

The Institute for Cancer Research, The Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111

An assay has been developed to measure the ability of human lymphocytes to repair damage to DNA. In this assay, purified human lymphocytes are exposed to graded doses of radiation and then stimulated with phytohemagglutinin to undergo DNA replication. The rate of incorporation of thymidine in irradiated lymphocytes during the second and subsequent rounds of DNA replication is taken to be indicative of the ability of the cells to repair damage to DNA. In lymphocytes from normal individuals, X-irradiation with doses of 100 to 800 rads was found to inhibit phytohemaglutinin-stimulated thymidine incorporation proportionally to the dose of radiation without curtailing the induction of DNA polymerase.

The response to phytohemagglutinin of lymphocytes from a patient with xeroderma pigmentosum after exposure to graded doses of X-irradiation was found to be similar to that of the normal controls, whereas the response after ultraviolet irradiation was markedly impaired. In contrast, lymphocytes from patients with ataxia telangiectasia were hypersensitive to X-irradiation. The data on these clinical syndromes support the idea that this assay measures DNA repair and indicates the feasibility of using this method for screening individuals for genetic deficits in DNA repair.

¹ This work was supported by USPHS Grants CA-06551, RR-05539, CA-11524, CA-15139, and CA-06927 from the NIH and by an appropriation from the Commonwealth of Pennsylvania.

² Present address: Department of Medicine, King George Medical College, Lucknow, India.

³ Also a member of the Department of Pathology, School of Medicine, University of Pennsylvania, Philadelphia, Pa. 19104.

Received 2/14/77. Accepted 7/11/77.