Immune escape mechanisms in ALCL

• anaplastic large cell lymphoma
• cytotoxic T cell
• apoptosis
• major histocompatibility complex
• serine protease inhibitor
• protease inhibitor 9

Systemic anaplastic large cell lymphoma (ALCL) is a CD30 positive T cell lymphoma with a broad spectrum of morphological, immune phenotypical, and clinical characteristics.¹ Two clinicopathological entities can be distinguished: anaplastic lymphoma kinase (ALK) positive systemic nodal ALCL and ALK negative systemic nodal ALCL. ALK expression, usually the result of a t(2;5) translocation, is related to a younger age, lower international prognostic index risk, and an excellent prognosis.^2–4 Similar to most other lymphomas, ALCLs harbour many non-neoplastic, in principle immune competent, lymphocytes. In immune competent patients, putative expression of tumour antigens in ALCL (or any other lymphoma) should, in principle, elicit an antitumour immune response. Indeed, it was shown recently that ALK can elicit a humoral antitumour immune response in ALK positive patients with ALCL and that functional anti-ALK CTL precursors are present within the peripheral T cell repertoire of healthy donors, clearly indicating that ALK is a tumour antigen.^5,6 In addition, the epithelial tumour antigen MUC1 (also known as EMA) is highly expressed in ALK positive ALCL,⁷ and MUC1 has been shown to elicit a MUC1 specific cytotoxic immune response in haematological malignancies.⁸ However, the very presence of tumour cells indicates that any antitumour immune response, whether humoral or cytotoxic, is apparently insufficient for the elimination of tumour cells. Assuming the presence of a specific antitumour immune response, this indicates that tumour cells have acquired mechanisms to escape from this immune response.

“In immune competent patients, putative expression of tumour antigens in anaplastic large cell lymphoma should, in principle, elicit an antitumour immune response”