WT1-Peptide Vaccination Shows High Immunogenicity and Clinical Activity in Patients with Acute Myeloid Leukemia.
Authors: Ulrich Keilholz , Scheibenbogen Carmen , Letsch Anne , Asemissen Anne Marie , Hofmann Wolf Karsten , Uharek Lutz , Wolfgang Blau , Eckhard Thiel 
Published: April 2020

BACKGROUND: The transcription factor Wilms tumor protein 1 (WT1) holds great promise for immunotherapy of leukemia. WT1 is strongly expressed in the majority of leukemic blasts, is essential for blast proliferation, and is spontaneously immunogenic.

METHODS: In the present phase II trial, 12 HLA-A2+ patients with AML without curative treatment option, were vaccinated with WT1.126–134 peptide mixed with adjuvant KLH as T-helper protein and GM-CSF 4 times bi-weekly, then monthly.

RESULTS: Patients characteristics, immune responses and clinical outcome are shown in table 1.

Patient characteristics, immunologic response, and clinical outcome Pat FAB/caryotype previous chemotherapy disease status at study onset no. of vaccinations clinical outcome WT1Tetr+ T cells in PB after vaccination WT1Tetr+ T cells in BM after vaccination *PB, peripheral blood; BM, bone marrow; MDS, myelodysplastic syndrome; MPD, myeloproliferative disease. 1 M4 yes 2.PR 15 CR 12 months 0.49% 0.87% 2 M2 11q23 yes 1.CR 18 cCR 30+ months 0.43% 0.91% 3 M2 no PD 4 SD 3 months 0.42% 0.80% 4 M6 yes PD 4 PD neg. neg. 5 M2 yes 1.PR 6 PD 0.37% 0.51% 6 M1 yes 2. PR 9 PD 0.43% 0.40% 7 M2 yes 2.PR 9 PD 2.00% 1.36% 8 M7 yes PD 4 PD neg. neg. 9 M5b yes 2.CR 12 cCR 8+ months 0.44% 0.33% 10 sAML from MDS no PD 12 SD 8 months 0.23% 0.13% 11 sAML from MPS no PD 12 SD 9+ months 0.22% 0.53% 12 M4 no PD 8 SD 3 months 1.11% 1.35%

WT1-specific T cells could be detected in 3 patients before vaccination. An induction or enhancement of a T cell response against WT1 was observed in 10 of 12 patients after 2 – 6 vaccinations ranging from 0.22 to 2.00% (median 0.43%) in peripheral blood and from 0.33 to 1.36% (median 0.80%) in bone marrow as analysed by tetramer and cytokine staining. At study onset 6 patients had progressive AML (PD) with 40 – 90% marrow blasts, 4 patients partial remission (PR) following chemotherapy and two patients complete remission (CR) at high risk for relapse. Four of the 6 patients with progressive AML had disease stabilization for 3, 3, 8 and 9 months, which is ongoing in the latter patient. Disease stabilization was accompanied by a decrease/normalization of peripheral blasts in two patients and a &gt;50% decrease in RBC transfusion requirements in a patient with AML evolved from MDS. One patient with PR at study onset had an early relapse and then achieved CR for 12 months (patient 1). Both patients vaccinated in CR are in continuous hematological CR (cCR) for 8+ and 30+ months (patient 2 and 9). The remaining 5 patients had PD after 4 – 9 vaccinations. Bone marrow WT1 RNA levels as molecular disease marker paralleled the clinical course as they decreased 1 – 2 logs in the 3 patients with CR or cCR after 6 vaccinations (Fig. 1A), stabilized or decreased in all 4 patients with SD (Fig. 1B), and increased 1 – 2 logs in 4 of the 5 patients with PD (Fig. 1B). No significant toxic effects were observed.

CONCLUSION: WT1 peptide vaccination can efficiently induce a specific immune response and has clinical activity in the absence of significant toxicity. These results warrant further studies of WT1 vaccination in AML patients at high risk for relapse.

Fig. 1 WT1 levels in bone marrow before and after 6 vaccinations in patients with CR or cCR (A), SD (B) or PD (C) after vaccination. Fig. 1. WT1 levels in bone marrow before and after 6 vaccinations in patients with CR or cCR (A), SD (B) or PD (C) after vaccination.