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Background: Whether human T-lymphotropic virus type 1 (HTLV-1) carriers can develop sufficient humoral immunity after coronavirus disease 2019 (COVID-19) vaccination is unknown., Methods: To investigate humoral immunity after COVID-19 vaccination in HTLV-1 carriers, a multicenter, prospective observational cohort study was conducted at five institutions in southwestern Japan, an endemic area for HTLV-1. HTLV-1 carriers and HTLV-1-negative controls were enrolled for this study from January to December 2022. During this period, the third dose of the COVID-19 vaccine was actively administered. HTLV-1 carriers were enrolled during outpatient visits, while HTLV-1-negative controls included health care workers and patients treated by participating institutions for diabetes, hypertension, or dyslipidemia. The main outcome was the effect of HTLV-1 infection on the plasma anti-COVID-19 spike IgG (IgG-S) titers after the third dose, assessed by multivariate linear regression with other clinical factors., Results: We analyzed 181 cases (90 HTLV-1 carriers, 91 HTLV-1-negative controls) after receiving the third dose. HTLV-1 carriers were older (median age 67.0 vs. 45.0 years, p < 0.001) and more frequently had diabetes, hypertension, or dyslipidemia than did HTLV-1-negative controls (60.0% vs. 27.5%, p < 0.001). After the third dose, the IgG-S titers decreased over time in both carriers and controls. Multivariate linear regression in the entire cohort showed that time since the third dose, age, and HTLV-1 infection negatively influenced IgG-S titers. After adjusting for confounders such as age, or presence of diabetes, hypertension, or dyslipidemia between carriers and controls using the overlap weighting propensity score method, and performing weighted regression analysis in the entire cohort, both time since the third dose and HTLV-1 infection negatively influenced IgG-S titers., Conclusions: The humoral immunity after the third vaccination dose is impaired in HTLV-1 carriers; thus, customized vaccination schedules may be necessary for them., (© 2024. The Author(s).)

Objective: Identifying the new integration of human T-lymphotropic virus type I (HTLV-I) proviral genome into initially uninfected cells after cocultivation with HTLV-I infected cells is important for clarifying the process of infection. We examined the usefulness of inverse long polymerase chain reaction (IL-PCR) for this purpose., Methods: An experimental system using IL-PCR was applied to detect the transmission of HTLV-I between irradiated HTLV-I infected cells (HUT102) and uninfected targed cells (MOLT4, K562) after short-term and long-term coculturing., Results: In every coculture experiment with irradiated HTLV-I infected cells and uninfected cells, the new integration of HTLV-I was easily identified by IL-PCR. Oligoclonal proliferation of HTLV-I-positive cells was shown among MOLT4 cells even 4 months after the cocultivation; however, no evidence of viral replication was observed by indirect immunofluorescence assay or reverse transcription-PCR. We also used IL-PCR to assess the inhibitory effects of azidothymidine, anti-gp46, anti-vascular cell adhesion molecule-1 and anti-heat shock cognate protein 70 (HSC70) monoclonal antibody. Integration of HTLV-I provirus was inhibited in all of these cases except for anti-HSC70., Conclusion: This experimental method enabled the detection of cell-to-cell transmission of HTLV-I directly and was useful for studying the mechanisms of cell-associated HTLV-I infection., (Copyright 2002 S. Karger AG, Basel)