Infection with Human T cell Leukemia Virus type 1 can be associated with myelopathy/tropical spastic paraparesis (HAM/TSP) and other inflammatory diseases. Lymphocytes from about half of Human T cell Leukemia Virus type 1-infected subjects spontaneously proliferate in vitro, and how this phenomenon relates to symptomatic disease and viral burden is poorly understood.

To evaluate T-cell proliferation in vitro among patients co-infected with Human T cell Leukemia Virus type 1/Hepatitis C Virus/Human Immunodeficiency Virus type 1.

From 610 Human T cell Leukemia Virus-infected patients of the Human T cell Leukemia Virus outpatient clinic from Institute of Infectious Diseases “Emilio Ribas” in São Paulo, 273 agreed to participate: 72 had HAM/TSP (excluded from this analysis) and 201 were asymptomatic, a classification performed during a regular neurological appointment. We selected the subgroup made up only by the 201 asymptomatic subjects to avoid bias by the clinical status as a confounder effect, who had laboratory results of Human T cell Leukemia Virus type 1 proviral load and T-cell proliferation assay in our database. They were further grouped according to their serological status in four categories: 121 Human T cell Leukemia Virus type 1 asymptomatic mono-infected carriers; 32 Human T cell Leukemia Virus type 1/Hepatitis C Virus, 29 Human T cell Leukemia Virus type 1/Human Immunodeficiency Virus type 1, and 19 Human T cell Leukemia Virus type 1/Human Immunodeficiency Virus type 1/Hepatitis C Virus co-infected patients. Clinical data were obtained from medical records and interviews. DNA Human T cell Leukemia Virus type 1 proviral load (PVL) and T-cell proliferation (LPA) assay were performed for all samples.

From a total of 273 subjects with Human T cell Leukemia Virus type 1, 80 presented co-infections: 29 had Human Immunodeficiency Virus type 1, 32 had Hepatitis C Virus, and 19 had Human Immunodeficiency Virus type 1 and Hepatitis C Virus. Comparing the groups based on their serological status, independently of being asymptomatic carriers, we observed a significant increase of PVL (p < 0.001) and LPA (p = 0.001). However, when groups were stratified according to their clinical and serological status, there was no significant increase in Human T cell Leukemia Virus type 1 PVL and LPA.

No significant increase of basal T-cell proliferation among Human T cell Leukemia Virus type 1 co-infected was observed. This interaction may be implicated in liver damage, worsening the prognosis of co-infected patients or, on the contrary, inducing a higher spontaneous clearance of Hepatitis C Virus infection in Human T cell Leukemia Virus type 1 co-infected patients.