Pathological features of diseases associated with human T‐cell leukemia virus type I

Abstract

In the early 1980s, the first human retrovirus, human T‐cell leukemia virus type I (HTLV‐I), was isolated and its characterization opened up the new field of human viral oncology. Adult T‐cell leukemia/lymphoma (ATLL), which is associated with HTLV‐I, is characterized clinically by the appearance of characteristic flower cells, a rapid clinical course, occasional skin lesions, lymphadenopathy and hepatosplenomegaly. Severe opportunistic infections are occasionally accompanied. In addition, HTLV‐I infection is associated with autoimmune and reactive disorders, such as HTLV‐I‐associated myelopathy and uveitis, and is also related to immunodeficient infectious diseases. Pathological findings of ATLL in the lymph nodes, skin, liver and other organs have been described. Common histological features are a diffuse proliferation of atypical lymphoid cells that vary in size and shape. In addition to ATLL, non‐neoplastic organopathies have been documented in many organs, such as the central nerve system, lung, skin, lymph nodes and gastrointestinal tract. To clarify the HTLV‐I‐associated diseases, it is important to understand the pathological variations. (Cancer Sci 2007; 98: 772–778)

Adult T‐cell leukemia/lymphoma (ATLL) is a human malignancy associated with a retrovirus, human T‐cell leukemia virus type I (HTLV‐I).^{( 1} , ^{2 )} The clonality of T cells with HTLV‐I proviral DNA integration changes from undetectable to polyclonal, and then further to monoclonal upon malignant transformation. Analysis of proviral DNA integrated into cellular DNA has shown that leukemic cells are always infected with HTLV‐I. These cells are also consistently monoclonal with respect to proviral integration, which indicates that they originate from a single cell infected with HTLV‐I.^{( 3} , ^{4 )} On the basis of findings related to changes in peripheral blood, the clinical stage is considered to gradually progress from carrier to smoldering, chronic and acute‐type leukemia.^{( 5 )}

In a previous series of studies, we and other groups characterized the histopathological changes in HTLV‐I‐associated lymph node lesions.^{( 6} , ⁷ , ⁸ , ⁹ , ¹⁰ , ¹¹ , ^{12 )} In addition to the typical adult T‐cell leukemia (ATL) lymphoma of pleomorphic and anaplastic large cell types, we identified lymph nodes with an unusual Hodgkin's disease‐like histology (Hodgkin‐like ATLL) in the HTLV‐I‐positive patients, and Hodgkin‐like ATLL showed prodromal clinical features.^{( 7 )} We also reported finding HTLV‐I‐associated lymphadenitis, a non‐neoplastic HTLV‐I‐associated lymph node lesion.^{( 9 )} Furthermore, in some cases of chronic‐ and smoldering‐type leukemia, atypical cells are usually small with irregular configurations.^{( 10 )}

Infection with HTLV‐I is a direct cause of ATLL, which can, via the induction of immunodeficiency, indirectly cause many other diseases, such as opportunistic lung infections, monoclonal gammopathy,^{( 13 )} chronic renal failure^{( 14 )} and strongyloidiasis.^{( 15 )} Studies conducted during the past 20 years have also demonstrated an association between the virus and a subset of chronic progressive myelopathies, known as HTLV‐I‐associated myelopathy/tropical spastic paraparesis (HAM/TSP).^{( 16} , ^{17 )} The development of HAM/TSP is linked to specific human leukocyte antigen haplotypes, as well as to disorders of organ systems other than the nervous system, including uveitis, alveolitis,^{( 18 )} Sjögren's syndrome,^{( 19 )} polymyositis^{( 20 )} and arthritis^{( 21 )} (Table 1). The fact that the provirus of HTLV‐I has been detected in the form of polyclonal integration in most of the patients with these diseases, especially HAM/TSP and strongyloidiasis, indicates that this virus is widespread among lymphocytes.^{( 22 )}

Table 1.

Human T‐cell leukemia virus type I (HTLV‐I)‐related diseases

Disorder	Type
Neoplastic
Peripheral blood (leukemia)	Smoldering type
	Chronic type
	Acute type
Lymph node (lymphoma)	Hodgkin's‐like type
	Pleomorphic small cell type
	Pleomorphic (medium and large cell) type
	Anaplastic large cell type
Skin	Erythema
	Papule
	Nodule
Gastrointetinal tract	Erosion
	Ulceration
	Tumor
Liver	Potal or sinus infiltration
Bone marrow	Infiltration with or without fibrosis
Reactive
Confirmed	HTLV‐I‐associated myelopathy
	HTLV‐I‐associated uveitis
	HTLV‐I‐associated lymphadenitis
Not‐confirmed	HTLV‐I‐associated bronchopneumopthy
	HTLV‐I‐associated arthropathy
	HTLV‐I‐associated nephropathy

Lymph node lesions

Histopathological examination of the HTLV‐I‐associated lymph nodes usually, although not uniformly, discloses a pleomorphic type. In addition to overt ATLL, some patients with preovert ATLL show a Hodgkin's disease‐like morphology and lymph nodes in non‐neoplastic carriers show features of lymphadenitis.^{( 7} , ^{9 , 23 )}

Lymphadenitis type.  Histological examination of the lymph nodes of HTLV‐I‐associated lymphadenitis shows a preserved nodal architecture with small lymph follicles, enlargement of the paracortex, and diffuse infiltration of small or intermediate‐size lymphocytes (Fig. 1a), with the latter cells showing slight nuclear irregularities. Immunohistochemically stained sections have shown proliferating small‐ to intermediate‐size lymphocytes possessing a peripheral helper or inducer T‐cell phenotype (CD1⁻, 2⁺, 3⁺, 4⁺, 8⁻), whereas no cases have shown rearrangement or deletion of the T‐cell receptor genes Cβ and Jγ, or rearrangement of the immunoglobulin heavy chain gene (JH). Except for a few cases, no monoclonal proviral DNA bands have been found. In a few cases, oligoclonal bands were detected. However, these bands were weaker than those of typical ATLL, probably because of the small population of HTLV‐I‐integrated lymphocytes.^{( 7 )}

Figure 1.

Histology of human T‐cell leukemia virus type I (HTLV‐I)‐associated lymphadenitis and Hodgkin‐like adult T‐cell leukemia/lymphoma (ATLL). (a) The lymph nodes of HTLV‐I‐associated lymphadenitis show enlarged paracortex with a diffuse infiltration of lymphocytes, which express the CD4 antigen (window). (b) The lymph nodes of Hodgkin‐like ATLL show Reed–Sternberg‐like giant cells, which reacted with CD30 antibody (window).

Hodgkin's‐like type.  The lymph nodes exhibit a relatively preserved nodal architecture with diffuse infiltration of small‐ or medium‐sized lymphocytes with mild nuclear irregularity. Small aggregated foci or clusters of a few giant cells with irregularly lobulated, highly convoluted Reed–Sternberg or Hodgkin's cell‐like nuclei are scattered throughout the expanded paracortex (Fig. 1b). The giant cells occasionally display mitotic features. In the immunohistological analysis, the proliferating small‐ to medium‐sized lymphocytes possess a peripheral T‐cell phenotype of helper or inducer cells (CD1⁻, 2⁺, 3⁺, 4⁺, 8⁻) and giant cells react with CD30 antibody or CD15. Receptor gene analysis has demonstrated rearrangement or deletion of the TCR gene Cβ or Jγ. Proviral HTLV‐1 DNA bands have been found, although the bands are weaker than those usually seen in typical ATLL, probably due to the small population of integrated HTLV‐1 lymphocytes. Molecular analysis of single‐cell polymerase chain reaction has confirmed that the giant cells are reactive cells, which specifically resemble the immature B cell lineage, whereas the background CD4⁺ T cells, which show evidence of clonality, are HTLV‐I infected.^{( 9} , ^{12 )}

Pleomorphic (medium and large cell) type.  The medium and large tumor cells vary in size and show a clear nuclear irregularity. Giant cells, with cerebriform, Reed–Sternberg type or bizarre nuclei, are frequently seen in these tissues (Fig. 2a). This type is typical nodal lesion of ATLL. Immunohistological evidence indicates that these tumor cells contain the peripheral T‐cell phenotype (CD1⁻, 2⁺, 3⁺, 45RO⁺ and usually CD4⁺), whereas receptor gene analysis has identified rearrangement or deletion of the TCR gene Cβ or Jγ. Proviral HTLV‐1 DNA bands have been detected in all cases.^{( 10} , ^{23 )}

Figure 2.

Histology of pleomorphic (medium and large cell) type, pleomorphic small cell type, anaplastic large cell type and angioimmunoblastic T‐cell lymphoma (AILT)‐like adult T‐cell leukemia/lymphoma (ATLL). (a) The pleomorphic (medium‐ and large‐sized cell) type shows a diffuse proliferation of atypical medium‐ to large‐sized lymphoid cells with irregular nuclei, intermingled with cerebriform giant cells (in the center). (b) The lymph nodes of pleomorphic small cell type show a diffuse proliferation of atypical medium‐ to small‐sized lymphoid cells. (c) Anaplastic large cell type shows a diffuse proliferation of atypical large lymphoid cells with prominent nucleoli. (d) AILT‐like ATLL shows proliferation of high endothelial venules with various infiltrating inflammatory cells.

Pleomorphic small cell type.  Histologically, these tumor cells are as large as or slightly larger than normal blood lymphocytes (Fig. 2b) and show mild nuclear irregularities, with only a few cells displaying mitotic features. Tumor cells are of the peripheral T‐cell phenotype and rearrangement or deletion of the TCR genes is present. Proviral HTLV‐1 DNA bands have been detected in all cases.^{( 10} , ^{23 )}

Anaplastic large cell type.  The tumor cells are much larger than the cells of large cell lymphoma and show a uniform pattern of cell proliferation. Tumor cells with prominent nucleoli and an abundant cytoplasm have been found, and multinucleated giant cells, such as Reed–Sternberg cells, have also been detected (Fig. 2c). Tumor cells containing CD30 antigen and peripheral T‐cell phenotype as well as rearrangement or deletion of the TCR genes have been detected, and proviral HTLV‐1 DNA bands have been detected in all cases.^{( 6} , ^{23 )}

Angioimmunoblastic T‐cell lymphoma‐like ATLL.  The rare morphological variant of ATLL includes the angioimmunoblastic T‐cell lymphoma (AILT)‐like type. The lymph nodes examined have shown proliferation of high endothelial venules and the presence of various infiltrating inflammatory cells, including plasma cells and eosinophils (Fig. 2d). The lymphoma cells are medium to large in size with clear cytoplasm.^{( 24 )} Tumor cells are of the peripheral T‐cell phenotype and rearrangement or deletion of the TCR genes is present. Proviral HTLV‐1 DNA bands have been detected in all cases. This type is rare.

Survival rates.  The median survival time (MST) and 2‐ and 5‐year survival rates are shown in Fig. 3 for the different groups of patients. Patients with lymph nodes of the Hodgkin's and pleomorphic small cell types show the highest MST and 2‐ and 5‐year survival rates. The pleomorphic (medium and large cell) type, which displays features typical of ATLL, has been associated with a rapidly deteriorating survival curve, both during the early and late stages of the disease (Fig. 3). The anaplastic large cell type and AILT type are also associated with a highly aggressive course as almost all patients have died within 2 years of diagnosis. Hodgkin's type was found to be associated with a progressive decrease in survival rate throughout an observation period of 8 years. Pleomorphic small cell type lymphoma has been associated with an initial steep increase in mortality, but the rate reaches a plateau during the mid and late period of observation. However, all cases with lymphadenitis were still alive at the end of one study (Fig. 3).^{( 23 )}

Figure 3.

Survival curve of human T‐cell leukemia virus type I (HTLV‐I)‐associated lymph node lesions. The pleomorphic (medium and large cell) type (n = 219) and anaplastic large cell type (n = 27) are associated with a rapidly deteriorating survival curve, whereas Hodgkin's type (n = 18) shows a progressive decrease in survival rate. Pleomorphic small cell type (n = 18) is associated with an initial steep increase in mortality that reaches a plateau during the middle and late periods of observation. In contrast, all cases with lymphadenitis (n = 14) were still alive at the end of the study concerned.

Cutaneous lesions

ATLL commonly involves the skin as well as the peripheral blood and lymph nodes. Cutaneous lesions related to ATLL are polymorphous in appearance, and in all clinical subtypes, skin lesions are frequently observed and their incidence reportedly varies from 43 to 72%.^{( 25 )} Furthermore, some reports have described patients who presented with only cutaneous lesions without either leukemic change or visceral invasion for many years.^{( 26} , ²⁷ , ²⁸ , ^{29 )} Johno et al. have proposed a new category, the cutaneous‐type ATLL (cATLL), representing persistent skin lesions observed throughout the entire course that do not easily develop into nodal lymphoma.^{( 26 )} They reported also that the prognosis of the tumoral type of cATLL (MST 26 months) is worse than that of the erythematopapular type (MST 80 months).^{( 26 )}

We previously examined the HTLV‐I proviral state and clinicopathological features of the cutaneous lesions of 80 cases with serum anti‐ATL antibody (ATLA) to clarify the correlation between macroscopic and histopathological findings and prognosis.^{( 29 )}

HTLV‐1 provirus status and features of cutaneous lesions.  The cutaneous lesions associated with ATLA‐positive cases have also been analyzed. The MST for patients with the provirus was found to be 14 months, which was markedly shorter than that for patients negative for proviral DNA integration (MST 72 months). In 46 cases with proviral DNA, 21 had solitary or multiple red nodules (including three with subcutaneous induration), eight had multiple red papules, and 17 had erythema (Fig. 4). Patients with papules and tumors tend to have poorer prognosis than those with erythema (Fig. 5). Histopathological examination of cases with erythema shows perivascular or diffuse infiltration of small‐ to medium‐sized atypical lymphoid cells with mild to moderate nuclear atypia in the upper dermis (Fig. 4). Mitotic features are few in number. These atypical lymphoid cells represent the peripheral T cell phenotype (CD1⁻, 2⁺, 3⁺, 45RO⁺ and usually CD4⁺).^{( 26} , ²⁷ , ²⁸ , ^{29 )} The histology of nodular infiltration pattern shows medium‐ to large‐sized atypical lymphoid cells with round or irregular nuclei and small nucleoli. Mitotic features are occasionally encountered. The diffuse infiltration pattern also shows atypical medium‐ to large‐sized lymphoid cells. The prognosis is poorer for patients with nodular or diffuse infiltration of medium‐ to large‐sized lymphoma cells than for those with perivascular infiltration of small‐ to medium‐sized lymphoma cells (Fig. 5). Furthermore, in the same group of 46 cases, 20 showed nodular infiltration, 17 diffuse infiltration, and nine perivascular infiltration (including two cases with a lichenoid or band‐like infiltration pattern).^{( 29 )}

Figure 4.

Macroscopic and histopathological findings of cutaneous lesions. The macroscopic findings have been classified as (a) erythema, (b) papules and (c) nodules. The histopathological findings have been classified as (d) perivascular infiltration of atypical lymphoid cells, (e) diffuse infiltration of medium‐ to large‐sized atypical lymphoid cells and (f) infiltration of large atypical lymphoid cells.

Figure 5.

Survival curve of cases with cutaneous lesions. Patients with papules (n = 8) and nodules (n = 21) have poorer prognosis than those with erythema (n = 17). Histopathological evidence shows that the prognosis is poorer for patients with nodular (n = 21) or diffuse (n = 17) infiltration of medium‐ to large‐sized lymphoma cells than for those with perivascular infiltration of small‐ to medium‐sized lymphoma cells (n = 9). HTLV‐I, human T‐cell leukemia virus type I.

Macroscopic findings have corresponded approximately to histological findings. In one study of cases with nodules, 18 cases showed nodular infiltration, three diffuse infiltration, and none perivascular infiltration, whereas of the cases with papules, two showed nodular infiltration, six diffuse infiltration, and none perivascular infiltration. Eight of the cases with erythema showed diffuse infiltration, nine showed perivascular infiltration and none showed nodular infiltration. Finally, patients with nodules and papules showed overall poor prognosis with an MST of 9 months for cases with nodules, 11 months for those with papules, and 32 months for those with erythema. In this series, patients with nodules and papules showed a poorer prognosis than those with erythema, and histological analysis showed that patients with nodular infiltration of atypical lymphoid cells had the poorest prognosis (MST 9 months). The prognosis for patients with diffuse infiltration (MST 20 months) was a little better than that for patients with perivascular infiltration (MST 24 months).^{( 29 )}

Bone marrow.  Involvement of the bone marrow is occasionally seen even in cases with leukemic blood pictures, as is patchy infiltration of atypical lymphoid cells with irregular or round nuclei in the marrow cavity, sometimes near the bone trabeculae. Clinically, hypercalcemia is an important laboratory finding related to ATLL. Absorption of bone accompanied by periosteal fibrosis, such as seen in osteitis fibrosa generalisata, may or may not be accompanied by infiltration of the tumor cells (Fig. 6a). Sometimes osteoclasts are increased in number.

Figure 6.

Histology of bone marrow, liver and stomach. (a) The bone marrow shows diffuse fibrosis with CD3⁺ lymphoma cells (window). (b) The portal area of the liver shows a diffuse infiltration of atypical lymphoid cells. (c) The stomach shows a tumorous lesion with a diffuse proliferation of lymphoma cells with anaplastic large cell features (window).

Liver

Involvement of the liver is mainly seen in the portal area, which shows infiltration of atypical medium‐ to large‐sized lymphoid cells with irregular nuclei, occasional destruction of limiting plates and in some cases sinus infiltration, but rarely fibrosis (Fig. 6b). Mitotic features are occasionally encountered.

Stomach

Recent studies have suggested that HTLV‐1 may also be involved in the development of gastric T‐cell lymphoma (GTL). Sakata and Kazuma reported that 23–78% of ATLL cases showed stomach invasion, and almost all of them were at an advanced clinical stage.^{( 30 )} Although these findings indicate a high frequency of gastric invasion by ATLL cells at advanced clinical stage, a few cases with early stage HTLV‐1‐associated GTL have also been reported.

We analyzed 14 patients with HTLV‐1‐associated GTL. GTL was located in the upper corpus in four of these cases, in the middle corpus in three cases, and was widely distributed in seven cases. Macroscopic examination showed that an ulcerated mass had formed in nine cases, four cases appeared to be eroded and the remaining two cases were protruded tumors. Histologically, five cases were identified as diffuse medium cell type, nine as diffuse pleomorphic medium‐ and large‐sized cell type, and the last case as anaplastic large cell type. The pleomorphic medium cell type shows a diffuse infiltration of atypical medium‐sized lymphoid cells with round or irregular nuclei. The pleomorphic medium‐ to large‐sized cell type shows a diffuse infiltration of atypical medium‐ to large‐sized lymphoid cells with irregular or round nuclei. The anaplastic large cell type shows a diffuse proliferation of atypical large to giant cells with round or lobulated nuclei, distinct nucleoli and abundant cytoplasm. Cohesive growth patterns are detected (Fig. 6c). In all three types, the destruction of gastric glands by lymphoma cell infiltration are obvious. The prognosis was poor for all patients as they died within 2 years of treatment. Four cases in this series showed no evidence of leukemic changes, but nine cases showed atypical lymphoid cells in peripheral blood (1–2% of lymphocytes were atypical lymphocytes). HTLV‐1‐associated GTL in HTLV‐1‐endemic areas should thus be managed with great care, even when leukemia is not detected.^{( 31 )}

HTLV‐I‐associated myelopathy/tropical spastic paraparesis

The association of TSP with HTLV‐I was first demonstrated in 1985.^{( 16 )} Other independent studies conducted in Japan also found an association between HTLV‐I and spastic paraparesis, and designated this entity HAM.^{( 17 )} The disease mainly affects the spinal cord, particularly the lateral and anterior columns, where bilateral loss of myelin and axon, occurring mainly along the tract, has been observed. Perivascular and parenchymal infiltration by lymphocytes and macrophages, as well as astrocytosis, has been observed in the white and gray matters of the spinal cord, whereas blood vessels in the spinal cord and in the subarachnoid space of the spinal cord showed hyalinoid thickening of media and adventitia associated with infiltration of lymphocytes (Fig. 7a).^{( 17} , ^{32 )} The lymphocytes show no nuclear atypia. Mitotic features are rarely encountered.

Figure 7.

Histology of human T‐cell leukemia virus type I (HTLV‐I)‐associated myelopathy (HAM) and immunodeficient disorders. (a) HAM mainly affects the spinal cord, particularly the lateral and anterior columns, with loss of myelin and axon accompanied by perivascular infiltration with lymphocytes (window) (Kluver–Barrera staining). (b) HTLV‐I‐associated bronchopneumopathy (HAB) display a proliferation of bronchial mucosa epithelium with an infiltration of lymphocytes. (c) Strongyloides stercoralis were detected in the gastric glands. (d) Pneumocystis carinii were identified in the alveolar spaces by means of Grocott staining. (e) Immunocytochemistry for FoxP3 in an adult T‐cell leukemia/lymphoma (ATLL) sample. The nuclei of the leukemic cells are diffusely positive for FoxP3.

HTLV‐I‐associated uveitis

Based on the seroepidemiological, clinical and virological data, it can be concluded that HTLV‐I is closely associated with a certain type of uveitis. Uveitis is a sight‐threatening inflammatory disorder affecting the intraocular tissues (iris, ciliary body, vitreous body, optic nerve, retina, choroids). Pathological observation has demonstrated that in HTLV‐I‐associated uveitis the intraocular tissues are infiltrated by a number of inflammatory cells, including lymphocytes and histiocytes. The lymphocytes show no nuclear atypia and mitotic features are rarely encountered.^{( 33 )}

HTLV‐I‐associated bronchopneumopathy or diffuse panbronchiolitis

Kimura et al. reported that some individuals with idiopathic interstitial pneumonia and diffuse panbronchiolitis possessed an anti‐ATLA antibody and postulated a relationship between HTLV‐I infection and idiopathic interstitial pneumonia and diffuse panbronchiolitis.^{( 34 )} Histologically, there is a proliferation of bronchial mucosa epithelium accompanied by thickening of the basement membrane and infiltration predominantly of lymphocytes together with some plasma cells, histiocytes and neutrophils into the epithelial layer and mucosa propria (Fig. 7b). The lymphocytes are usually small, and nuclear atypia and mitotic features are rare, whereas in the alveolar areas there is mild fibrosis and edema of the wall as well as infiltration of lymphocytes and some plasma cells.^{( 35 )} In cases of leukemia/lymphoma infiltration, however, diffuse infiltration of atypical lymphocytes with irregular nuclear lymphocytes is prominent, and nodular proliferation is also present in these cases.

Immunodeficiency disorders

Infection with HTLV‐I is a direct cause of ATLL, and can also indirectly cause many other diseases via the induction of immunodeficiency, such as opportunistic lung infections (e.g. Pneumocystis carinii, cytomegalovirus, Aspergillus fumigatus and Cryptococcus neoformans), monoclonal gammopathy,^{( 13 )} chronic renal failure^{( 14 )} and strongyloidiasis (Fig. 7c,d).^{( 15 )}

ATLL is an aggressive neoplastic disease and usually exhibits a CD4⁺ CD25⁺ phenotype. In the HTLV‐I carrier states, CD4⁺ CD25⁺ lymphocytes increase in number, and regulatory T cells (Treg) are characterized by coexpression of CD4 and CD25. We analyzed the expression of forkhead/winged helix transcription factor (FoxP3), known to be important for Treg cell function and as a specific marker of Treg cells, on ATLL cells. FoxP3 expression was detected in the nuclei of the lymphoma cells in over half of the cases (Fig. 7e).^{( 36} , ^{37 )} This result demonstrates the association of ATLL with Treg, and may be related to immunodeficient infectious diseases in ATLL and HTLV‐I carriers.

Conclusion

ATLL is a useful system for understanding multistep tumorigenesis and developing strategies for its treatment. In addition, HTLV‐I infection is in fact associated with autoimmune and reactive disorders, and may be directly related to immunodeficient infectious diseases. HTLV‐I infections also constitute a useful tool for understanding host immunity. ‘ATLL‐ology’ can thus open wide a window onto human oncology, virology and immunology.