Azathioprine-induced carcinogenesis in mice according to Msh2 genotype.

BACKGROUND: The thiopurine prodrug azathioprine is used extensively in cancer therapy. Exposure to this drug results in the selection of DNA mismatch repair-deficient cell clones in vitro. It has also been suggested that thiopurine drugs might constitute a risk factor for the emergence of human neoplasms displaying microsatellite instability (MSI) because of deficient DNA mismatch repair. METHODS: Azathioprine was administered via drinking water (6-20 mg/kg body weight per day) to mice that were null (Msh2⁻(/)⁻; n = 27), heterozygous (Msh2(+/)⁻; n = 22), or wild type (Msh2(WT); n = 18) for the DNA mismatch repair gene Msh2. Control mice (45 Msh2⁻(/)⁻, 38 Msh2(+/)⁻, and 12 Msh2(WT)) received drinking water lacking azathioprine. The effect of azathioprine on tumorigenesis and survival of the mice was evaluated by Kaplan-Meier curves using log-rank and Gehan-Breslow-Wilcoxon tests. Mouse tumor samples were characterized by histology and immunophenotyping, and their MSI status was determined by polymerase chain reaction analysis of three noncoding microsatellite markers and by immunohistochemistry. Msh2 status of tumor samples was assessed by loss of heterozygosity analyses and sequencing after reverse transcription-polymerase chain reaction of the entire Msh2 coding sequence. All statistical tests were two-sided. RESULTS: Most untreated Msh2(WT) and Msh2(+/)⁻ mice remained asymptomatic and alive at 250 days of age, whereas azathioprine-treated Msh2(WT) and Msh2(+/)⁻ mice developed lymphomas and died prematurely (median survival of 71 and 165 days of age, respectively). Azathioprine-treated Msh2(+/)⁻ mice developed diffuse lymphomas lacking Msh2 expression and displaying MSI due to somatic inactivation of the functional Msh2 allele by loss of heterozygosity or mutation. By contrast, azathioprine-treated Msh2(WT) mice displayed no obvious tumor phenotype, but histological examination showed microscopic splenic foci of neoplastic lymphoid cells that retained Msh2 expression and did not display MSI. Both untreated and azathioprine-treated Msh2⁻(/)⁻ mice had a reduced lifespan compared with untreated Msh2(WT) mice (median survival of 127 and 107 days of age, respectively) and developed lymphomas with MSI. CONCLUSION: Azathioprine-induced carcinogenesis in mice depends on the number of functional copies of the Msh2 gene.

Adoptive transfer of T lymphocytes sensitized against the prion protein attenuates prion invasion in scrapie-infected mice.

There is to date no effective way of preventing or curing neurodegenerative diseases such as Alzheimer disease or transmissible spongiform encephalopathies. The idea of treating those conditions by immunological approaches has progressively emerged over the last ten years. Encouraging results have been reported in Alzheimer disease and in peripheral forms of mouse prion diseases following passive injection of Abs or active immunization against the peptides or proteins presumably at the origin of those disorders. Still, major difficulties persist due to some characteristics of those conditions such as slow evolution, brain location, uncertainties regarding precise pathogenic pathways, and, above all, the fact that the target Ag is self, meaning that it is poorly immunogenic and potentially harmful if tolerance was transgressed. To analyze some of those difficulties, we are developing adoptive cell transfer approaches. In this study, lymphocytes sensitized against the prion protein in nontolerant Prnp(-/-) mice were transferred into histocompatible wild-type recipients which were partly or totally devoid of their own lymphocytes. Under such conditions, we found that the engrafted T lymphocytes resisted peripheral tolerance, remained reactive for several months against epitopes of the prion protein, and significantly attenuated the progression of prions in secondary lymphoid organs with subsequent delay in the evolution of the neurological disease. Interestingly, those protective T lymphocytes secreted lymphokines and migrated more readily into the host CNS but did not appear to be engaged in cooperation with host B cells for Ab production.