Background: B2001X (NCT03123939) is a multicenter global study of tisa to provide access to patients (pts) with r/r ALL including prior anti-CD19 therapy after enrollment ended in the pivotal ELIANA (NCT02435849) study. We report clinical outcomes and cellular kinetics in B2001X including pts with prior BLINA exposure or INO as bridging therapy (BT). Methods: Eligible pts ≤21 y at diagnosis with ≥2 relapse, refractory or post allogeneic transplant (alloSCT) relapse were enrolled globally. Results: As of Nov 4, 2019, 73 pts were enrolled; 67 received tisa. 91% received lymphodepletion. Among 65 pts ≥3 mo follow up (FU) or discontinued earlier (efficacy analysis set [EAS]) median FU was 9.6 mo (range [R] 0.2-16.5). Median age 10 y (R 2-33); prior alloSCT 61%; 15 pts had prior BLINA and 9 pts had INO as BT. Efficacy is summarized in Table. 13/14 relapsed pts were medullary (isolated or combined with extramedullary [EM]) and 1 EM; 9 within 6 mo including 4/5 who were CD19(+). 64% had CRS (G 3/4 13%/15%; Penn scale); 24% had neurologic events (G 3/4 9%/2%; CTCAE v4.03). 4 deaths ≤30 d: 2 early ALL progression, 1 fatal CRS with refractory ALL, 1 infection with multiorgan failure. Transgene level in peripheral blood: limited to no in vivo expansion in nonresponders (n=8) vs responders (n=42). Median duration of persistence (T last) of tisa was 272 d (R 27-379) in responders. In pts with CR/CRi, C_max (geo-mean [CV%]) and median T last were 9260 (124) copies/µg DNA and 154 d (R 28-349), respectively, in pts who received INO as BT (n=6) vs 38,500 (215) and 273 d (R 27-379), respectively, in pts with no INO as BT (n=36). Conclusions: Outcomes in B2001X remain consistent with ELIANA. In pts with prior BLINA or INO as BT, a trend toward suboptimal outcomes was observed but should be interpreted with caution due to small n, short FU and potential confounding factors. Clinical trial information: NCT03123939

^a3 pts with no CR/CRi, 5 early progression, 2 deaths precluding disease evaluation.

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