The hepatic niche leads to aggressive natural killer cell leukemia proliferation through the transferrin-transferrin receptor 1 axis.

Aggressive natural killer cell leukemia (ANKL) is a rare lymphoid neoplasm frequently associated with Epstein-Barr virus, with a disastrously poor prognosis. Owing to the lack of samples from patients with ANKL and relevant murine models, comprehensive investigation of its pathogenesis including the tumor microenvironment (TME) has been hindered. Here we established 3 xenograft mice derived from patients with ANKL (PDXs), which enabled extensive analysis of tumor cells and their TME. ANKL cells primarily engrafted and proliferated in the hepatic sinusoid. Hepatic ANKL cells were characterized by an enriched Myc-pathway and proliferated faster than those in other organs. Interactome analyses and in vivo CRISPR-Cas9 analyses revealed transferrin (Tf)-transferrin receptor 1 (TfR1) axis as a potential molecular interaction between the liver and ANKL. ANKL cells were rather vulnerable to iron deprivation. PPMX-T003, a humanized anti-TfR1 monoclonal antibody, showed remarkable therapeutic efficacy in a preclinical setting using ANKL-PDXs. These findings indicate that the liver, a noncanonical hematopoietic organ in adults, serves as a principal niche for ANKL and the inhibition of the Tf-TfR1 axis is a promising therapeutic strategy for ANKL.

Humoral and cellular immune response to second and third severe acute respiratory syndrome coronavirus 2 mRNA vaccine in patients with plasma cell dyscrasia.

BACKGROUND: The recently developed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccine has a short history of use and further information is needed regarding its efficacy, especially in immunocompromised conditions, such as plasma cell dyscrasia (PCD). METHODS: We retrospectively measured serum SARS-CoV-2 antibodies against the spike protein (S-IgG) after the second and third mRNA vaccine doses (doses 2 and 3, respectively) in 109 patients with PCD. We evaluated the proportion of patients with an adequate humoral response (defined as S-IgG titers ≥300 antibody units/mL). RESULTS: Although active anti-myeloma treatments prior to vaccination had a significantly negative impact on adequate humoral response, specific drug subclasses including immunomodulatory drugs, proteasome inhibitors, and monoclonal antibodies were not negatively associated, except for B-cell maturation antigen-targeted therapy. Dose 3 (booster vaccination) led to significantly higher S-IgG titers and more patients acquired an adequate humoral response. Furthermore, evaluation of vaccine-induced cellular immune response in patients using T-spot Discovery SARS-CoV-2 kit, revealed an enhanced cellular immune response after Dose 3. CONCLUSIONS: This study highlighted the significance of booster SARS-CoV-2 mRNA vaccination in patients with PCD with respect to humoral and cellular immunity. Moreover, this study highlighted the potential impact of certain drug subclasses on vaccine-induced humoral immune response.

Case report: Genomic analysis of a therapy-related chronic myelomonocytic leukemia with KMT2A rearrangement that progressed to acute myeloid leukemia with acute promyelocytic leukemia-like features.

We report a 69-year-old female who was a human T-cell leukemia virus type 1 carrier and exhibited a unique clinical course of developing three hematological malignancies within a short period: diffuse large B-cell lymphoma (DLBCL), chronic myelomonocytic leukemia (CMMoL), and acute myeloid leukemia (AML). Although the blast cells in AML showed typical morphological and immunophenotypical features of acute promyelocytic leukemia (APL), it did not harbor RARα gene fusion and thus initially diagnosed as APL-like leukemia (APLL). The patient developed heart failure with a fulminant clinical course and died soon after the diagnosis of APLL. Retrospective analysis with whole-genome sequencing detected a chromosomal rearrangement between KMT2A and ACTN4 gene loci both in CMMoL and APLL samples, but not in the DLBCL sample. Therefore, CMMoL and APLL were considered to be derived from the same clone with KMT2A translocation associated with prior immunochemotherapy. However, KMT2A rearrangement is rarely found in CMMoL in general and ACTN4 is also a rare partner of KMT2A translocation. Thus, this case did not follow typical transformational process of CMMoL or KMT2A-rearranged leukemia. Importantly, additional genetic alterations, including NRAS G12 mutation, were found in APLL, but not in CMMoL samples, suggesting that they might contribute to leukemic transformation. This report highlights the diverse effects of KMT2A translocation and NRAS mutation on the transformation of hematological cells as well as the importance of upfront sequencing analysis to detect genetic backgrounds for a better understanding of therapy-related leukemia.

A comprehensive evaluation of humoral immune response to second and third SARS-CoV-2 mRNA vaccination in patients with malignant lymphoma.

More information is needed regarding the efficacy of SARS-CoV-2 mRNA vaccines in immunocompromised populations, including patients with malignant lymphoma. This study aimed to evaluate humoral responses to the second and third mRNA vaccine doses in 165 lymphoma patients by retrospective analysis of serum SARS-CoV-2 spike protein antibody (S-IgG) titers. Patients with S-IgG titers ≥ 300, 10-300, and ≤ 10 binding antibody units (BAU)/mL were defined as adequate responders, low responders, and non-responders, respectively. S-IgG titers > 10 BAU/mL were considered to indicate seroconversion. After the second dose, 56%, 16%, and 28% of patients were adequate responders, low responders and non-responders, respectively. Multivariate analysis revealed that being an adequate responder after the second dose was associated with receiving the vaccine > 12 months after last chemotherapy, total peripheral lymphocyte count of ≥ 1000/µL, estimated glomerular filtration rate of ≥ 50 mL/min/1.73 m2, and vaccine type (mRNA-1273). After the third dose, patients had significantly higher S-IgG titers and a greater proportion achieved seroconversion. With this third dose, 26% of second-dose non-responders achieved seroconversion and 68% of second-dose low responders became adequate responders. Subsequent SARS-CoV-2 mRNA vaccinations may elicit an immune response in immunocompromised patients who do not initially respond to vaccination.

Recurrent pain attacks during romiplostim treatment in a patient with ITP carrying a heterozygous MEFV mutation.

We report a case of recurrent pain attacks during romiplostim treatment in a woman with immune thrombocytopenia carrying a heterozygous MEFV mutation. Five months after starting treatment with romiplostim for immune thrombocytopenia, she was diagnosed with idiopathic pericarditis. She was switched to eltrombopag, but thrombocytopenia did not improve. Romiplostim was restarted 7 months later, although she then developed recurrent right hypochondrial pain. The pain typically occurred three days after the romiplostim injection and resolved two days later. She had never experienced such recurrent pain before starting romiplostim or after discontinuing it. Genetic analysis showed that she carried a heterozygous R202Q alteration in exon 2 of the MEFV gene. MEFV mutation is known to cause familial Mediterranean fever, which is characterized by symptoms such as recurrent fever, abdominal and chest pain, arthritis, and pericarditis. This case suggests that romiplostim has the potential to trigger recurrent pain/inflammation attacks in individuals with systemic inflammatory abnormalities.

CCR7 alterations associated with inferior outcome of adult T-cell leukemia/lymphoma under mogamulizumab treatment.

Adult T-cell leukemia/lymphoma (ATL) patients have a very poor prognosis. The humanized anti-CCR4 therapeutic monoclonal antibody, mogamulizumab, is a key agent for ATL treatment. Our previous integrated molecular analysis demonstrated that among all the driver genes in ATL, CCR7 gene alterations were significantly associated with clinical response to mogamulizumab. Accordingly, here we investigated the detailed clinical impact of CCR7 alterations in a larger cohort of ATL patients. These CCR7 alterations, most of which lead to C-terminus truncations, were observed in 27 of 223 patients (12%). For patients receiving mogamulizumab but not allogeneic hematopoietic stem cell transplantation (HSCT), CCR7 alterations were significantly associated with worse survival (median survival from the first dose of mogamulizumab of 0.7 years for 12 patients with CCR7 alterations vs. 1.6 years for 72 patients without, p = 0.020). On the other hand, the presence or absence of CCR7 alterations had no significant impact on survival in the entire cohort (median overall survival of 1.4 and 1.8 years, respectively, p = 0.901), or on the survival of patients receiving allogeneic HSCT (median survival from the day of transplantation of 0.9 years for 6 patients with CCR7 alterations and 1.4 years for 48 without, p = 0.543). Multivariate analysis indicated that patients with CCR4 alterations but lacking CCR7 alterations (n = 20) had significantly better survival after receiving mogamulizumab-containing treatments (hazard ratio for survival, 0.437, 95% confidence interval, 0.192-0.994). This study contributes to the establishment of precision medicine for ATL.

A novel RARA-SNX15 fusion in PML-RARA-positive acute promyelocytic leukemia with t(11;17;15)(q13;q21.2;q24.1).

Acute promyelocytic leukemia (APL) is characterized by a series of retinoic acid receptor (RAR) fusion genes that lead to the dysregulation of RAR signaling and onset of APL. PML-RARA is the most common fusion generated from t(15;17)(q24;q21). In addition, the reciprocal fusion RARA-PML is present in over 80% of t(15;17) APL cases. The bcr3 types of RARA-PML and RARA-PLZF in particular are reciprocal fusions that contribute to leukemogenesis. Here, we report a variant APL case with t(11;17;15)(q13;q21.2;q24.1). Massive parallel sequencing of patient RNA detected the novel fusion transcripts RARA-SNX15 and SNX15-LINC02255 along with the bcr3 type of PML-RARA. Genetic analysis revealed that RARA-SNX15L is an in-frame fusion due to intron retention caused by RNA mis-splicing. RARA-SNX15L consisted mainly of SNX15 domains, including the Phox-homology domain, which has a critical role in protein-protein interactions among sorting nexins and with other partners. Co-immunoprecipitation analysis revealed that RARA-SNX15L is directly associated with SNX15 and with itself. Further studies are needed to evaluate the biological significance of RARA-SNX15L in APL. In conclusion, this is the first report of APL with a complex chromosomal rearrangement involving SNX15.

Acute Promyelocytic Leukemia in a Patient With Chronic Continuous Type of Crohn's Disease.

Chronic inflammation can induce leukemogenic mutations in hematopoietic stem cells (HSCs). We report a case of acute promyelocytic leukemia (APL) in a patient with chronic continuous type of Crohn's disease. The patient had been diagnosed with Crohn's disease at the age of 28 years and had received conventional treatments with biologics, but not azathioprine. At the age of 51, he was diagnosed with APL with ider(17). Long-term exposure to chronic continuous inflammation from Crohn's disease might be a factor inducing genomic instability in HSCs, which lead to the subsequent development of APL. APL is a rare hematological manifestation that required attention in Crohn's disease patients.

Genomic determinants impacting the clinical outcome of mogamulizumab treatment for adult T-cell leukemia/lymphoma.

In order to identify genomic biomarkers for the outcome of mogamulizumab-containing treatment, an integrated molecular analysis of adult T-cell leukemia/lymphoma (ATL) was conducted on 64 mogamulizumab-naïve patients. Among driver genes, CCR4 and CCR7 alterations were observed in 22% and 11% of the patients, respectively, both consisting of single nucleotide variants (SNV)/insertion-deletions (indels) in the C-terminus. Patients with CCR4 alterations or without CCR7 alterations exhibited a more favorable clinical response (complete response [CR] rate 93%, 13/14; P=0.024, and CR rate 71%, 40/56; P=0.036, respectively). Additionally, TP53, CD28, and CD274 alterations were identified in 35%, 16%, and 10% of the patients, respectively. TP53 alterations included SNV/indels or copy number variations (CNV) such as homozygous deletion; CD28 alterations included SNV, CNV such as amplification, or fusion; CD274 alterations included CNV such as amplification, or structural variants. Univariate analysis revealed that TP53, CD28 or CD274 alterations were associated with worse overall survival (OS) (hazard ratio [HR]: 2.330, 95% confidence interval [CI]: 1.183-4.589; HR: 3.191, 95% CI: 1.287- 7.911; HR: 3.301, 95% CI: 1.130-9.641, respectively) but that CCR4 alterations were associated with better OS (HR: 0.286, 95% CI: 0.087-0.933). Multivariate analysis indicated that in addition to performance status, TP53, CCR4 or CD274 alterations (HR: 2.467, 95% CI: 1.197-5.085; HR: 0.155, 95% CI: 0.031-0.778; HR: 14.393, 95% CI: 2.437-85.005, respectively) were independently and significantly associated with OS. The present study contributes to the establishment of precision medicine using mogamulizumab in ATL patients.

Management of hepatitis B virus (HBV) reactivation in patients with resolved HBV infection based on a highly sensitive HB core-related antigen assay.

AIMS: To prevent hepatitis B virus (HBV) reactivation-related hepatitis, we examined the clinical usefulness of a highly sensitive HB core-related antigen (iTACT-HBcrAg) assay in patients with resolved HBV infection after nucleos(t)ide analog (NA) treatment for HBV reactivation. METHODS: We retrospectively analyzed 27 patients with resolved HBV infection who experienced HBV reactivation (defined as HBV DNA levels of 1.3 log IU/ml or more), and who received systemic chemotherapies for hematological malignancies between 2008 and 2020. iTACT-HBcrAg, HBsAg-HQ, and antibodies against hepatitis B surface antigen (anti-HBs) were measured using samples stored after HBV reactivation. The lower limit of quantification for iTACT-HBcrAg was 2.0 log U/ml. RESULTS: HBV reactivation was diagnosed at a median HBV DNA level of 1.8 log IU/ml, and then all patients received NA treatment. No patient had HBV-related hepatitis with a median maximum HBV DNA level of 2.0 log IU/ml. The positivities of iTACT-HBcrAg and HBsAg-HQ were 96% and 52% after HBV reactivation, respectively. Of 25 patients with detectable iTACT-HBcrAg at the initiation of NA treatment, 17 (68%) achieved iTACT-HBcrAg loss. Median durations from NA treatment to HBV DNA loss and iTACT-HBcrAg loss or the last follow-up were 35 and 175 days, respectively. Recurrence of HBV reactivation after NA cessation was not observed in seven of eight patients who achieved iTACT-HBcrAg loss or seropositive for anti-HBs during follow-up, except for one without anti-HBs after allogeneic transplantation. CONCLUSIONS: iTACT-HBcrAg could be a potential surrogate marker for diagnosing early-stage HBV reactivation as well as safe cessation of NA treatment in patients with resolved HBV infection after HBV reactivation.

Clinicopathological significance of CD28 overexpression in adult T-cell leukemia/lymphoma.

CD28, one of the costimulatory molecules, has a pivotal role in T-cell activation, and its expression is strictly regulated in normal T cells. Gain-of-function genetic alterations involving CD28 have been frequently observed in adult T-cell leukemia/lymphoma (ATLL). These abnormalities, such as CD28 fusions and copy number variations, may not only confer continuous, prolonged, and enhanced CD28 signaling to downstream pathways but also induce overexpression of the CD28 protein. In this study, 120 ATLL cases were examined by immunohistochemistry for CD28 and its ligands CD80 and CD86, and their expression on tumor cells was semiquantitatively evaluated. CD28 was overexpressed in 55 (46%) cases, and CD80 or CD86 (CD80/CD86) was infrequently overexpressed in 12 (11%). Compared with non-overexpressers, CD28 overexpressers showed a higher frequency of CD28 genetic alterations and had an increased number of CD80/CD86-positive non-neoplastic cells infiltrating tumor microenvironment. In the entire ATLL patient cohort, CD28 overexpressers showed a significantly poorer overall survival (OS) compared with non-overexpressers (P = .001). The same was true for a subgroup who were treated with multidrug regimens with or without mogamulizumab. CD28 overexpression had no prognostic impact in the group who received allogeneic hematopoietic stem cell transplantation. In the multivariate analysis for OS, CD28 overexpression was selected as an independent risk factor. These results suggest ATLL patients with CD28 overexpression have more aggressive clinical course and are more refractory to treatment with multidrug chemotherapy. CD28 overexpression appears to be a novel unfavorable prognostic marker in ATLL patients, and further prospective studies are warranted to establish its prognostic significance.

Clinical significance of the immunoglobulin G heavy-chain repertoire in peripheral blood mononuclear cells of adult T-cell leukaemia-lymphoma patients receiving mogamulizumab.

'Monitoring of immune responses following mogamulizumab-containing treatment in patients with adult T-cell leukaemia-lymphoma (ATL)' (MIMOGA) is a multicentre prospective clinical study (UMIN000008696). In the MIMOGA study, we found that a lower percentage of CD2- CD19+ B cells in peripheral blood mononuclear cells (PBMC) was a significant unfavourable prognostic factor for overall survival (OS). Accordingly, we then analysed the immunoglobulin G (IgG) heavy-chain repertoire in PBMC by high-throughput sequencing. Of the 101 patients enrolled in the MIMOGA study, for 81 a sufficient amount of PBMC RNA was available for repertoire sequencing analysis. Peripheral IgG B cells in patients with ATL had a restricted repertoire relative to those in healthy individuals. There was a significant positive correlation between the Shannon-Weaver diversity index (SWDI) for the IgG repertoire and proportions of B cells in the PBMC of the patients. Multivariate analysis identified two variables significantly affecting OS: a higher serum soluble interleukin-2 receptor level, and a lower SWDI for the IgG repertoire [hazard ratio, 2·124; 95% confidence interval, 1·114-4·049; n = 44]. The present study documents the importance of humoral immune responses in patients receiving mogamulizumab-containing treatment. Further investigation of strategies to enhance humoral immune responses in patients with ATL is warranted.

Clinical significance of TP53 mutations in adult T-cell leukemia/lymphoma.

Adult T-cell leukaemia/lymphoma (ATL) patients have a poor prognosis. Here, we investigated the impact of TP53 gene mutations on prognosis of ATL treated in different ways. Among 177 patients, we identified 47 single nucleotide variants or insertion-deletions (SNVs/indels) of the TP53 gene in 37 individuals. TP53 copy number variations (CNVs) were observed in 38 patients. Altogether, 67 of 177 patients harboured TP53 SNVs/indels or TP53 CNVs, and were categorized as having TP53 mutations. In the entire cohort, median survival of patients with and without TP53 mutations was 1·0 and 6·7 years respectively (P < 0·001). After allogeneic haematopoietic stem cell transplantation (HSCT), median survival of patients with (n = 16) and without (n = 29) TP53 mutations was 0·4 years and not reached respectively (P = 0·001). For patients receiving mogamulizumab without allogeneic HSCT, the median survival from the first dose of antibody in patients with TP53 mutations (n = 27) was only 0·9 years, but 5·1 years in those without (n = 42; P < 0·001). Thus, TP53 mutations are associated with unfavourable prognosis of ATL, regardless of treatment strategy. The establishment of alternative modalities to overcome the adverse impact of TP53 mutations in patients with ATL is required.

Immunohistochemistry for CCR4 C-terminus predicts CCR4 mutations and mogamulizumab efficacy in adult T-cell leukemia/lymphoma.

Mogamulizumab targets extracellular N-terminal domain of CCR4, which is expressed in most adult T-cell leukemia/lymphoma (ATL) cases. Recently, we reported that CCR4 C-terminal gain-of-function mutations were frequent in ATL cases, and a subgroup with these mutations who were treated without allogenic hematopoietic stem cell transplantation (HSCT) and with mogamulizumab-containing [HSCT (-) and mogamulizumab (+)] regimens had a superior survival rate. Although these mutations are most likely a biomarker for predicting a strong response to mogamulizumab, their detection is time-consuming and costly. A more convenient screening tool may be necessary in the clinical setting. In this study, the clinicopathological importance of immunohistochemistry for the CCR4 N-terminus (CCR4-N-IHC) and C-terminus (CCR4-C-IHC) was examined in a large ATL cohort (n = 92). We found that CCR4-C-IHC, but not CCR4-N-IHC, was inversely correlated with the CCR4 mutation status. In ATL patients negative for CCR4-C-IHC, a subgroup treated with HSCT (-) and mogamulizumab (+) regimens showed a significantly better prognosis. In addition, CCR4-C-IHC was found to be a useful marker for high-sensitivity screening of the CCR4 mutational status (87%). The present study suggests that CCR4-C-IHC may be useful for identifying ATL patients harboring mutated CCR4 who may benefit from the superior efficacy of mogamulizumab-containing regimens and that CCR4-C-IHC may be a rapid and cost-efficient tool for screening for CCR4 mutation status.

Volunteer unrelated donor cell-derived acute myeloid leukemia with RUNX1-RUNX1T1.

A 15-year-old male was diagnosed with acute myeloid leukemia with t(6;9)(p23;q34), a chimeric DEK-NUP214 fusion gene. He underwent allogeneic bone marrow transplantation (allo-BMT) from an unrelated volunteer donor at first molecular remission. Approximately 5 years after allo-BMT, multiple bone marrow aspirations showed increased blasts to 63%, which were positive for myeloperoxidase, CD13, CD33, CD56, and CD34. Surprisingly, t(8;21)(q22;q22.1), a chimeric RUNX1-RUNX1T1 (not DEK-NUP214) fusion gene, was detected with full donor chimerism. To our best knowledge, this is the first case of a volunteer unrelated donor cell-derived acute myeloid leukemia harboring a chimeric RUNX1-RUNX1T1 fusion gene.

Clinical significance of CD28 gene-related activating alterations in adult T-cell leukaemia/lymphoma.

Multiple oncogenic events are involved in the development of adult T-cell leukaemia/lymphoma (ATL). Because CD28 plays a pivotal role in T-cell activation, we focused on alterations of the CD28 gene in ATL. We found multiple genetic abnormalities related to CD28 among the 144 patients enrolled in the present study. These involved gene fusions with the cytotoxic T-lymphocyte-associated antigen 4 or the inducible T-cell co-stimulator in 14 patients (10%), CD28-activating mutations in 3 (2%), and CD28 copy number variations in 34 (24%). Patients with such CD28 gene alterations were significantly younger than those without. In patients not receiving allogeneic haematopoietic stem cell transplantation, those with CD28 gene alterations tended to have a worse prognosis than those without. Finally, patients with chronic or smouldering ATL subtypes with CD28 gene alterations had a significantly worse prognosis than those without. These findings indicate that ATL, especially chronic or smouldering subtypes, have a more aggressive clinical course and are more refractory to conventional chemotherapies or mogamulizumab if they harbour CD28 gene alterations, likely because of continuous, prolonged, and enhanced CD28 activatory signalling. Novel treatment strategies to overcome the effects of these CD28 gene alterations are warranted.

Mogamulizumab for adult T-cell leukemia-lymphoma: a multicenter prospective observational study.

Monitoring of Immune Responses Following Mogamulizumab-Containing Treatment in Patients with Adult T-Cell Leukemia-Lymphoma (ATL) (MIMOGA) is a multicenter prospective observational study to establish the most effective and safe treatment strategy using mogamulizumab for ATL patients (UMIN000008696). Mogamulizumab-naive patients were enrolled (n = 102), of whom 101 received mogamulizumab-containing treatment (68 acute, 18 lymphoma, 12 chronic, and 3 smoldering subtypes). At enrollment, there was a significant inverse correlation between serum soluble interleukin-2 receptor (sIL-2R) levels and percentages of Tax-specific cytotoxic T lymphocytes (Tax-CTLs) in the entire lymphocyte population or in the CD8+ T cell subset, but there was not a correlation with cytomegalovirus pp65-specific cytotoxic T lymphocytes (CMV-CTLs). The overall response rate was 65%, and median progression-free survival and overall survival (OS) were 7.4 and 16.0 months, respectively. A higher percentage of Tax-CTLs, but not CMV-CTLs, within the entire lymphocyte population or in the CD8+ T cell subset was significantly associated with longer survival. Multivariate analysis identified the clinical subtype (acute or lymphoma type), a higher sIL-2R level, and a lower percentage of CD2-CD19+ B cells in peripheral blood mononuclear cells as significant independent unfavorable prognostic factors for OS. This indicates that a higher percentage of B cells might reflect some aspect of a favorable immune status leading to a good outcome with mogamulizumab treatment. In conclusion, the MIMOGA study has demonstrated that mogamulizumab exerts clinically meaningful antitumor activity in ATL. The patient's immunological status before mogamulizumab was significantly associated with treatment outcome. Further time series immunological analyses, in addition to comprehensive genomic analyses, are warranted.

Clinical significance of tryptophan catabolism in follicular lymphoma.

The enzyme, indoleamine 2,3-dioxygenase 1 (IDO), catabolizes tryptophan (Trp) in the kynurenine (Kyn) pathway, and is important in suppressing antitumor immune responses in the tumor microenvironment. With regard to previously untreated patients with follicular lymphoma (FL), we sought to establish the prognostic significance of Trp catabolism in this disease. Serum Trp and Kyn levels in 110 patients with FL were quantified, and their relationship to different clinical parameters studied. IDO expression in the lymph nodes of affected patients was studied. Study participants included 54 males and 56 females (age range 39-86, median 62 years), showing a 5-year overall survival (OS) rate of 78.5%. Patients with a high Kyn level (5-year OS, 65.0% vs. 81.7%; p = 0.026), high Kyn/Trp ratio (71.1% vs. 81.7%; p = 0.002), and low hemoglobin (Hb) level (<12.0 g/dL; p = 0.001; a component of FL international prognostic indexes) demonstrated a significantly shorter OS. Multivariate analysis included the following 10 variables: age, sex, serum ß2-microglobulin, Hb, longest diameter of the largest involved node, Ann Arbor stage, serum lactate dehydrogenase, histologic grading, B symptoms, and serum Kyn/Trp ratio; a lower Hb level and a high Kyn/Trp ratio (HR, 3.239; 95% CI, 1.296-8.096) led to a significantly inferior OS. In the microenvironment, some CD11c-positive myeloid dendritic cells but not FL tumor cells were found to produce IDO. Overall, measuring levels of serum Kyn and Trp in individual patients with FL contributed to predicting their prognosis.