T-cell prolymphocytic leukemia (T-PLL)

T-PLL is usually suspected when a blood test shows a very high lymphocyte count, usually above 100,000 per microliter, often with a large spleen, liver or lymph nodes. The first tests are a complete blood count and a look at the cells under a microscope (blood smear). Flow cytometry (immunophenotyping) then reads markers on the cells. T-PLL cells are mature T cells that carry markers such as CD3, CD5 and CD7, and more than 9 in 10 contain a protein called TCL1.

Genetic tests help confirm it. Chromosome tests (cytogenetics) and FISH look for changes on chromosome 14 or the X chromosome that switch on the TCL1 gene family. A T-cell receptor test checks that the T cells all come from one abnormal cell (clonality). An international expert group diagnoses T-PLL when enough of these findings are present together, including more than 5,000 T-PLL cells per microliter of blood or marrow.

Before treatment, a CT scan of the neck, chest, belly and pelvis shows swollen lymph nodes and organ size. A bone marrow biopsy is not usually needed to make the diagnosis, but it is used later to confirm a remission. People from countries where the HTLV-1 virus is common are tested for it, because a virus-linked T-cell leukemia can look similar.

Active T-PLL is usually treated first with alemtuzumab, an antibody given through a vein that attaches to a marker called CD52 on T cells. In studies of first treatment, more than 9 in 10 people responded, and an international expert group recommends a course of about 10 to 12 weeks. In one small study where it was given under the skin instead, it worked much less well. Because it strongly lowers immune defenses, infection prevention and monitoring are part of treatment.

The response rarely lasts: in an international consensus report, disease control after alemtuzumab typically lasted about 8 to 11 months. That is why experts recommend that people who respond well be considered, where feasible, for an allogeneic stem cell transplant to consolidate, or strengthen, that response. About a third may achieve long-term survival this way, but relapse and transplant complications remain serious risks.

A smaller number of people have instead had high-dose chemotherapy followed by a return of their own stem cells. A European registry study found this can lengthen disease control, especially after alemtuzumab, but its authors wrote that it probably is not a cure. Other medicines, including pentostatin, bendamustine and venetoclax combinations, have been used after relapse or in trials, but responses tend to be short, and a 2024 phase 2 study found only limited benefit from ibrutinib plus venetoclax.

When a transplant from a donor is planned, the team usually tests brothers and sisters first. Each full sibling has about a one in four chance of being a full match.

Most patients do not have a matched relative. In the words of NMDP, the U.S. registry, “75% of patients don’t have a fully matched donor in their own family.” The team then searches registries of volunteer donors around the world and banks of donated cord blood. In some transplants, a half-matched parent, child or sibling can also be the donor.

Matching depends on inherited tissue markers called HLA, so a patient is most likely to match someone who shares their ancestry. Every person who joins makes the search a little more likely to succeed, especially for patients from groups that are underrepresented on registries.

T-PLL is a serious leukemia, and medicines alone rarely control it for long. First treatment with alemtuzumab works for most people, but the effect usually fades, often within a year or two. Treatments after a relapse tend to work only for a short time.

The biggest factors are whether the leukemia responds to first treatment and whether a donor transplant is possible. An international expert group says about a third of people who have a donor transplant after a complete remission may live long-term. Age and overall fitness also matter. In German registry data, people aged 80 or older lived a much shorter time than younger people. In a large transplant registry study, being over 60 and weaker overall fitness were linked to lower survival after transplant.

Registry numbers describe groups, not any one person. In a Dutch national study, long-term survival did not improve over two decades, and researchers say new kinds of treatment are needed.