The Frequency, Diversity, and Function of Human T-Cell Leukemia Virus Type 1-Specific CD8+ T-Cell Is Reduced in Adult T-Cell Leukemia Patients.
Authors: Kozako Tomohiro , Akimoto Masaki , Masamoto Izumi , Yoshimitsu Makoto , Matsushita Kakushi , Suzuki Shinsuke , Uozumi Kimiharu , Arima Naomichi 
Published: April 2020

Abstract
Human T-cell lymphotropic virus type 1 (HTLV-1)-specific CTL are thought to be immune effectors that reduce the risk of adult T-cell leukemia (ATL). However, in vivo conditions of anti-HTLV-1 CTL before and after ATL development have yet to be determined. To characterize anti-HTLV-1 CTL in asymptomatic HTLV-1 carriers (AC) and ATL patients, we analyzed the frequency and diversity of HTLV-1-specific CD8+ T cells in PBMC of 35 AC and 32 ATL patients using 16 distinct epitopes of HTLV-1 Tax or Env/HLA tetramers along with intracellular cytolytic effector molecules (IFN-γ , perforin, and granzyme B). Overall frequency of subjects possessing Tax-specific CD8+ T cells was significantly lower in ATL than AC (53% vs. 90%, p &lt; 0.001) whereas the difference in Env-specific CD8+ T cells was not statistically significant. AC possessed Tax11-19/HLA-A*0201-specific tetramer+ cells by 90% and Tax301-309/HLA-A*2402-specific tetramer+ cells by 92%. Some AC recognized more than one epitope. In contrast, ATL recognized only Tax 11-19 with HLA-A*0201 and Tax301-309 with HLA-A*2402 at frequencies of 30% and 55%. There were also significant differences in percentage of cells binding Tax11-19/HLA-A*0201, Tax301-309/HLA-A*2402, and CMV/HLA tetramers between AC and ATL. Anti-HTLV-1 Tax CD8+ T cells in AC and ATL produced IFN-γ in response to Tax. Contrarily, perforin and granzyme B expression in anti-HTLV-1 CD8+ T cells of ATL was significant lower than that of AC, but no differences in anti-CMV CD8+ T cells. In addition, expression of perforin and granzyme B in HTLV-1 Tax tetramer+/CD8+ T lymphocytes were diminished in comparison to those in CMV tetramer+/CD8+ T lymphocytes in both AC and ATL. Frequency of Tax-specific CD8+ T cells in AC were related with proviral load in HLA-A*0201. These results suggest that our HTLV-1/HLA tetramer assay enabled analysis of anti-HTLV-1 CD8+ T cells in PBMC of AC and ATL patients and demonstrated deletion of anti-Tax CD8+ T cells in ATL patients. Intracellular cytokine expression in anti-HTLV-1 CD8+ T cells had significant difference between AC and ATL, but not in anti-CMV CD8+ T cells. The reduced frequency, diversity, and function of anti-HTLV-1 Tax CD8+ T cell clones may be related to the development of ATL. This HLA tetramer assay can be used for monitoring the in vivo status of CTL and it may be possible to identify the high risk group in AC of developing to ATL.
Summary of HTLV-1-specific tetramer and HTLV-1 proviral load in AC and ATL patients AC ATL †The number of subject positive for tetramers; the percentage of HTLV-1/HLA tetramer+/CD8+ T cells in the CD8+/CD45+ T lymphocytes &gt; 0.1% are counted as subject positives for tetramer. ††The HTLV-1 proviral load is the ± S.E., copies/1000 PBMC. *p &lt; 0.001; **p &lt; 0.05, Significant differences between AC and ATL. Subjects positive for Tax tetramer† 28 (n = 31) 15 (n = 28) * Subjects positive for Env tetramer† 4 (n = 31) 0 (n = 28) Tax11-19 tetramer+ CD8+ T cells† 9 (n = 10) 3 (n = 10) ** Tax301-309 tetramer+ CD8+ T cells† 22 (n = 24) 12 (n = 22) * HTLV-1 proviral load†† 65.4 ± 7.4 (n = 35) 1095.4 ± 194.1 (n = 29) *