Less than 12 hours af­ter re­veal­ing a flop on its sec­ond shot for al­pha-1 an­tit­rypsin de­fi­cien­cy, Ver­tex plowed ahead with an­oth­er da­ta drop from its part­ner­ship with CRISPR Ther­a­peu­tics. And though the topline proved pos­i­tive, con­cerns over con­di­tion­ing agents con­tin­ue to linger over the col­lab­o­ra­tion, as well as the en­tire gene ther­a­py space.

Pre­sent­ing da­ta from two tri­als at the Eu­ro­pean Hema­tol­ogy As­so­ci­a­tion an­nu­al meet­ing, the pair an­nounced that fol­low-up da­ta of at least three months for 22 pa­tients with ge­net­ic blood dis­or­ders in­di­cat­ed a “con­sis­tent and sus­tained” re­sponse to the ex­per­i­men­tal drug CTX001. All 15 pa­tients with trans­fu­sion-de­pen­dent be­ta tha­lassemia did not need fur­ther blood trans­fu­sions and all sev­en with se­vere sick­le cell dis­ease were pain free, the biotechs an­nounced.

There was one pa­tient not in­clud­ed in the da­ta cut­off of March 30, how­ev­er, who ex­pe­ri­enced a cere­bel­lar he­m­or­rhage less than three months af­ter be­ing treat­ed. The se­ri­ous side ef­fect was re­lat­ed to the busul­fan con­di­tion­ing gene ther­a­py pa­tients un­der­go be­fore re­ceiv­ing treat­ment, Ver­tex said, and has since re­solved.

Busul­fan has long proved tricky for com­pa­nies de­vel­op­ing gene ther­a­pies, with the chemo reg­i­men prov­ing a nec­es­sary but in­ten­sive process for pa­tients. It’s been linked in the past to can­cer and some have linked it to po­ten­tial cas­es of leukemia and myelodys­plas­tic syn­drome seen in blue­bird bio’s gene ther­a­py stud­ies.

Ad­di­tion­al­ly, as Ver­tex and CRISPR had pre­vi­ous­ly re­vealed, one be­ta tha­lassemia pa­tient ex­pe­ri­enced four se­ri­ous side ef­fects re­lat­ed or pos­si­bly re­lat­ed to CTX001. They all oc­curred with­in the con­text of an in­flam­ma­to­ry re­sponse and have al­so re­solved.

In the be­ta tha­lassemia study, in­ves­ti­ga­tors fol­lowed the 15 pa­tients for a range of four to 26 months, and the sick­le cell pa­tients from five to 22 months. Sev­en from across both stud­ies are more than a year out since re­ceiv­ing treat­ment. Fri­day’s re­sults are an up­date to a da­ta cut from De­cem­ber’s ASH con­fer­ence, which had on­ly in­clud­ed 10 pa­tients.

The gene ther­a­py in ques­tion, be­ing de­vel­oped joint­ly by Ver­tex and CRISPR, is an au­tol­o­gous ex vi­vo CRISPR/Cas9 treat­ment. Ver­tex teamed up with CRISPR back in 2015, but the pair ex­pand­ed on their part­ner­ship in April in a bid to de­vel­op the treat­ment more quick­ly.

In the ex­pan­sion, Ver­tex paid an ad­di­tion­al $900 mil­lion cash to take an­oth­er 10% of fu­ture sales from the gene edit­ing ther­a­py, with CRISPR hand­ing over re­spon­si­bil­i­ty for com­mer­cial­iz­ing CTX001 in the US. Along with oth­er re­cent changes to their part­ner­ship, the move ef­fec­tive­ly hands Ver­tex re­spon­si­bil­i­ty for man­u­fac­tur­ing the ther­a­py and stew­ard­ing it past reg­u­la­tors across the globe.

Should CTX001 be­come the first CRISPR-based ther­a­py to hit the mar­ket, that wa­ger would give Ver­tex a sig­nif­i­cant sales ad­van­tage over ri­vals like blue­bird. The Nick Leschly-run com­pa­ny has faced an up­hill climb for its gene ther­a­py pro­grams, ul­ti­mate­ly split­ting it­self in­to two com­pa­nies at the be­gin­ning of the year.

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