Chicago (Reuters) – Mixed results over the weekend from closely watched studies combining Bristol-Myers Squibb Co’s cancer immunotherapy with Nektar Therapeutics experimental drug NKTR-214, led at least one Wall Street analyst to reassess expectations.

Bristol agreed in February to pay Nektar $1.85 billion for a global development and profit-sharing deal aimed at increasing the effectiveness of Opdivo by combining it with immune response booster NKTR-214 for 20 cancer indications across nine different tumor types, including melanoma, kidney and lung cancers.

Dr. Adi Diab, from Houston’s MD Anderson Cancer Center and a lead trial investigator, presented updated early stage results at the American Society of Clinical Oncology annual meeting in Chicago showing that 11 out of 13, or 85 percent, of melanoma patients treated with Opdivo and NKTR-214 had tumor shrinkage, but the response rate fell to 50 percent after 14 additional patients were enrolled in the trial.

For kidney cancer, the addition of more trial patients lowered the response rate to 46 percent from 64 percent.

Diab said he expected the response rates to improve over time. But the presentation did not include an update on lung cancer patients treated so far.

Bristol and Nektar said they planned to move forward with late-stage studies of the combination for patients with melanoma, renal cell carcinoma and urothelial cancer.

“For now we are taking a more conservative view … although we continue to see potential for long-term value creation with ‘214,” JP Morgan analyst Jessica Fye said in a research note on Sunday.

Fye lowered her 2018 price target for Nektar shares, which closed at $90.35 on Friday, to $78 from $90, citing a more conservative estimate for NKTR-214’s potential in lung cancer.

Evercore ISI analyst Umer Raffat said that even though trial response rates had dropped, he believed the collaboration made sense for Bristol-Myers.

(Reporting by Deena Beasley; Editing by Peter Cooney)