Syncytium inducing viral phenotype halves thymic T cell production in children

HIV-1-infected children with syncytium-inducing (SI) viral strains have CD4+ T cell counts and thymic output levels approximately half as high as those in children with non-SI (NSI) viral strains, according to a new study.

Researchers in Madrid, Spain, compared the thymic production of new T cells in 90 samples from HIV-1-infected children, average age 4.9 years. They also looked at CD4+ T cell levels in the children, and their correlation with thymic output.

Children infected with SI viral strains had CD4+ T cell and thymic output levels approximately half as high as those observed in children with NSI viral strains (p < 0.001). Moreover, these differences were independent of viral load (which was similar in the SI and NSI groups), patient age and treatment type, report Drs Rafael Correa and Angeles Munoz-Fernandez, of the Hospital General Universitario -Gregorio Maranon. –

In three children followed prospectively, the switch from the NSI to the SI viral phenotype was followed by marked declines in both thymic output and CD4+ T cell levels.

-These results suggest an inhibitory effect of SI viral phenotype on the production of new T cells, – the authors say in the October 19th issue of AIDS, -which is independent of viral load and viral replication kinetics. – This conclusion is consistent with prior studies indicating that T-tropic (SI) viruses but not M-tropic (NSI) viruses are capable of infecting immature thymocytes.

– It is likely, – the investigators believe, – that disease progression in children, which is associated with the appearance of T-tropic viruses, could be due to the inhibition of thymic function produced by these viral strains, which would impede the recovery of lost CD4+ T cells. –

-This fact, – they conclude, -provides an additional rationale to implement antiretroviral therapies that lead to undetectable viral load levels, even in children with severe CD4+ T cell depletion, with the goal of allowing an adequate thymic function to recover lost T cells. –