University of Virginia Health System

Large Granular Lymphocyte (LGL) Leukemia (Syndrome)

Large granular lymphocyte (LGL) leukemia (syndrome)- Peripheral blood smear, Wright-Giemsa stain, 1000x

Introduction:

By light microscopy, large granular lymphocytes (LGLs) comprise about 10-20% of lymphocytes in the peripheral blood of normal individuals. Approximately 95% are natural killer (NK) cells and 5% are CD3+, CD8+ T cells. Polyclonal increases are seen in asplenia (Kelemene, et al. Clin Exp Immunol 63:696, 1986.) Polyclonal expansion of NK cells also occurs during pregnancy (Moffett-King A. Nat Rev Immunol 2:656, 2002), and in response to infections, particularly viral infections (French AR, et al. Curr Opin Immunol 15:203, 2003; Hislop ND, et al. Annu Rev Immunol 25:587, 2007), malignancy, allotransplants and autoimmune disorders (Parham P. Nat Rev Immunol 5:201, 2005).

Clonality can be demonstrated in the great majority of cases with LGL leukemia. Other terms that have been used to describe these disorders include LGL syndrome, T-gamma lymphocytosis, and lymphoproliferative disease of granular lymphocytes. Even though some 95% of normal LGLs in the peripheral blood are NK cells, the majority of the LGL leukemias are of the CD3+, CD8+ subset, and are CD57+. 

Description:

The clonal cells cannot be distinguished from normal large granular lymphocytes by light microscopy. A monotonous appearance of the cells favors a clonal process. In some cases of LGL leukemia the clonal cells are not all that large, but have the characteristic cytoplasmic azurophilic granules. Immunophenotyping and molecular genetic studies are necessary to establish a diagnosis, and determine the subset involved (T versus NK), and clonality.

LGLs are usually 1½-2 times the size of normal small peripheral blood lymphocytes, have more abundant clear to light grey cytoplasm, and demonstrate characteristic cytoplasmic azurophilic granules, often with a clearing around the granules giving a "halo" effect. The number of granules per cell is quite variable. The nucleus may be round, oval, or slightly indented, and the nuclear chromatin is mature with variable clumping. Nucleoli usually are not visible.

On a bone marrow aspirate the cells may be missed because the granules are not as visible, and the cells appear smaller with less cytoplasm.

Immunophenotypic and Molecular Genetic Studies:

• NK cell LGL (NK-LGL) subset- CD56+, CD16+, CD3-, CD57-
• T cell LGL (T-LGL) subset- CD8+, CD3+, CD57+, CD56-, CD4-

The presence or absence of CD56, CD57, CD3 and CD8 is the most important immunophenotypic profiling to aid in distinguishing between the T versus NK subsets. Overlap does occur, particularly with both the CD56 and CD57 markers, and often requires molecular genetic studies to differentiate.

If CD3 is positive, this identifies the T cell subset, but to prove clonality, a pcr-DNA study to document rearrangement of the TCR is necessary. If the CD3 is negative, whether there is overlap with the CD56 and CD57 markers or not, NK cell clonality can be determined by the pattern of expression of the killer immunoglobulin-like receptors (KIRs) by the cells.

Cytogenetics:

No signature cytogenetic abnormalities have been identified in either the NK or T cell subtypes.

Differential Diagnosis:

Because of the essentially diagnostic morphologic appearance of LGLs on a Wright-Giemsa stained peripheral blood smear, there is little need for a listing of other possible diagnoses. An occasional patient with acute lymphoblastic leukemia, especially those that are Philadelphia chromosome positive, will have cytoplasmic granules, but the immaturity of the nuclear chromatin, the presence of nucleoli, and the higher nuclear:cytoplasmic ratio serves to easily distinguish between the two.

A similar clinical and laboratory picture often occurs in patients with a leukemic phase of marginal zone B cell lymphoma and splenic lymphoma with villous lymphocytes. Both are B cell lymphoproliferative disorders which can be verified by immunophenotyping. Marginal zone B cells have an almost identical morphologic appearance as LGLs, but lack the azurophilic granules. Villous lymphocytes are small with a high nuclear:cytoplasmic ratio, scant cytoplasm and the characteristic polar, hair-like projections. Hairy cell leukemia often presents with a similar picture, and can easily be differentiated by both morphologic and immunophenotypic features.

Clinical and Laboratory Manifestations and their Management:

The clinical and laboratory manifestations of the T-LGL leukemia are, in almost all cases, due to associated autoimmune disorders. Autoimmune neutropenia is, by far, the most common finding, with an incidence of 75% or more. As a result, infections are seen, particularly in those cases with absolute neutrophil counts (ANCs) below 500/mm³. A point that needs to be made is that the incidence of infections at any ANC value is less in these patients and other patients with autoimmune neutropenia than when the neutropenia is due to decreased production. Autoimmune thrombocytopenia (ITP), autoimmune hemolytic anemia (AIHA), and pure red cell aplasia (PRCA) are also seen, but less frequently. Other autoimmune disorders are also quite common, especially rheumatoid arthritis. The rheumatoid factor is positive in over 50% and the ANA in up to 40%. A clinicopathologic picture identical to Felty's syndrome is not that infrequent. Splenomegaly is found in up to 50%, but lymphadenopathy is distinctly unusual.

Despite the frequent occurrence of autoimmune disorders, the great majority of patients with T-LGL leukemia are relatively asymptomatic and the course of the disease is quite chronic, with survival for decades. When infections are a problem, G-CSF (Neupogen or Neulasta) is very effective in reversing the neutropenia. Treatment of ITP and AIHA should be the same as in idiopathic cases (e.g. prednisone, IVIg). PRCA usually responds to cyclosporine, as do the autoimmune cytopenias. Treatment directed at the leukemic process per se is usually not an issue.

In the NK-LGL leukemia subset the course often is more aggressive and the clinical manifestations are more frequently due to the proliferative process (e.g. lymphadenopathy, hepatosplenomegaly, other organ involvement, B symptoms), and response to various chemotherapeutic agents is poor. Not all NK-LGL leukemias are aggressive. Those manifested only by lymphocytosis are often chronic, similar to the T-LGL, and may also be complicated autoimmune disorders (Blood 84:2721, 1994.)

General References:

• Keren DF, McCoyd JP, Carey JL (eds). Flow cytometry in clinical diagnosis, 3rd ed. Chicago, ASCP Press, 2001
• Loughan Jr TP. Clonal diseases of large granular lymphocytes. Blood 82:1, 1993
• Dhodapkar MU, Li CY, Lust JA, et al. Clinical spectrum of clonal proliferations of T-large granular lymphocytes: a T cell clonopathy of undetermined significance? Blood 84:1620, 1994
• Lamy T, Loughran Jr TP. Large granular lymphocytic leukemia. Cancer Control 5:25, 1998
• Kelemen E, Gergely P, Lehoczky D, et al. Permanent large granular lymphocytosis in the blood of splenectomized individuals without concomitant increase of in vitro natural killer cell cytotoxicity. Clin Exp Immunol 63: 696, 1986
• Parham P. MHC class I molecules and KIRS in human history, health and survival. Nat Rev Immunol 5:201, 2005
• Robertson MJ, Ritz J. Biology and clinical relevance of human natural killer cells. Blood 76:2421, 1990
• Moffett-King A. Natural killer cells and pregnancy. Nat Rev Immunol 2:656, 2002
• French AR, Yokoyama WM. Natural killer cells and viral infections. Curr Opin Immunol 15:203, 2003
• Hislop ND, Taylor GS, Sauce D, Rickinson AB. Cellular responses to viral infection in humans: lessons from Epstein-Barr virus. Annu Rev Immunol 25:587, 2007
• Tefferi A, Li CY, Witzig TE, et al. Chronic natural killer cell lymphocytosis: a descriptive clinical study. Blood 84:2721, 1994

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