Biotech investors wait on pins and needles for companies to report how their experimental drugs are faring in clinical studies. When the updates aren't great, biotech stocks can tank. But when the results are good, the stocks can take off in a big way.

Three biotech stocks that soared last week on positive pipeline updates were Adverum Biotechnologies (NASDAQ: ADVM), Iovance Biotherapeutics (NASDAQ: IOVA), and MeiraGTx Holdings (NASDAQ: MGTX). Here are the details on why these stocks performed so well and whether they're smart picks to buy now.

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1. Adverum Biotechnologies

The removal of a negative can also be a big positive. That's the story for Adverum Biotechnologies. Its stock skyrocketed 38% after the biotech announced on Thursday that the FDA lifted a clinical hold on one of the patient cohorts in a phase 1 clinical study evaluating ADVM-022 in treating wet age-related macular degeneration.

Adversum now expects to begin dosing of its second cohort in the study in June. Results from patients in the first cohort were so robust that it now intends to use a dose three times lower.

The phase 1 study of ADVM-022 isn't totally in the clear, though. The FDA still has a partial clinical hold in effect for dosing patients in the third cohort of the study. Adverum intends to work with the FDA to resolve all remaining issues in the way of moving forward with this third cohort.

2. Iovance Therapeutics

Iovance Therapeutics was the second biggest biotech winner last week, jumping nearly 36%. On Wednesday, Iovance reported promising interim data from clinical studies evaluating two of its experimental immunotherapies, both of which are based on the company's tumor-infiltrating lymphocyte (TIL) technology.

Let's start with the good news for LN-145. Patients with advanced cervical cancer taking the experimental TIL drug in a phase 2 clinical study achieved an objective response rate (ORR) of 44%. ORR refers to the proportion of patients with tumors that shrank by a predetermined amount. How good was this performance? It was a lot better than Merck's blockbuster cancer drug, Keytruda, which achieved an ORR of only 14% in previously treated advanced cervical cancer patients.

Then there's LN-144, also known as lifileucel. Patients with advanced melanoma in one of the cohorts of Iovance's phase 3 study who received lifileucel after checkpoint inhibitors failed achieved an ORR of 38%. And after a 7.4-month median follow-up, melanoma had progressed in only four out of 21 responders.