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Little is known about the efficacy of COVID-19 vaccines during acute lymphoblastic leukemia therapy (ALL); data for COVID-19 vaccine immune responses in pediatric leukemia remain sparse. We used flow cytometry and TCR sequencing to assess Spike Reactive T-cell responses in 20 patients aged 5-25 years undergoing Acute lymphoblastic leukemia (ALL) chemotherapy who had received COVID-19 vaccination. TCR sequencing was also done on T-cells from 5 COVID-19 vaccinated healthy adult individuals (healthy controls). Spike reactive T-cells (SRT) were detected by flow cytometry in 9 of 20 (45%) vaccinated patients undergoing ALL chemotherapy. Sequencing revealed public CD4+ and CD8+ TCR sequences reactive to epitopes across the Spike Protein in these patients. In conclusion, COVID-19 vaccination induced T-cell responses in a substantial fraction of children and young adults undergoing ALL chemotherapy.