Billionaire Patrick Soon-Shiong’s clinical stage immunotherapy firm NantKwest Inc. has only been public for about a month, but it’s been on a steady slide ever since – one that started well before the recent market downturn and that wasn’t halted by the ensuing rally.

The company, which makes a proprietary line of the immune system’s “natural killer” cells that are used to treat infectious, inflammatory diseases and cancer, went public July 28 at $25 a share and finished its first day of trading up big at nearly $35. That gave the company a market cap at the time of $3.7 billion.

Since that big IPO pop, though, the stock has fared poorly. For the week ended Aug. 26, shares were down 25 percent to $19.30 – notable not only because that made the company the biggest loser on the LABJ Stock Index, but because it was one of the few local stocks that didn’t get a bump last Wednesday, a day that saw markets rally after a week of big losses. (See page 32.)

The stock’s poor performance also comes despite analysts from Citigroup, Jefferies and others having recently initiated coverage of NantKwest, and most analysts give the stock a “buy” rating – and target prices well above $30 a share.

Biren Amin, a managing director and senior equity research analyst at New York’s Jefferies who follows the company, said he’s not sure why NantKwest’s stock has continued to sink and didn’t get a piece of last week’s rally. But he remains bullish about the company’s prospects, saying the drugs under development could be used in a broad patient population.

He rates NantKwest shares a “buy” with a $33 price target. What’s more, in an Aug. 24 note to investors, Amin said he expects the company to initiate a handful of clinical trials over the next few months, and those trials could further validate the prospects for NantKwest’s drugs.