It's an unusual day when one of the top names in late-breaking market news is a stock that doesn't yet exist. That would be Corteva Agriscience, the DowDuPont (NYSE:DD) offshoot that is yet to begin trading on its own. That hasn't prevented it from making headlines in the after-market, though.

Outside of that, noted clinical-stage biotech Inovio Pharmaceuticals (NASDAQ:INO) is taking a hard smack on the head following a development with a crucial (and deep-pocketed) partner.

Read on for more on these happenings, and how they're affecting the relevant stocks.

A stock trading board.

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The new kid on the S&P 500

Here's a deal: two S&P 500 companies for the price of one!

That's essentially what shareholders of chemicals giant DowDuPont will soon be getting, without having to move a muscle. It was announced late today by the influential index's owner, S&P Global, that Corteva, a spinoff of DowDuPont's agricultural products business, will become an S&P 500 component in early June.

Corteva displaces engineering and construction major Fluor (NYSE:FLR) from the S&P 500. Fluor will be knocked down to the S&P MidCap 400 index. In that index, Fluor will take the slot currently occupied by real estate services company Realogy Holdings. Finally, Realogy will become part of the S&P SmallCap 600, replacing oil and gas drilling concern Pioneer Energy Services.

The Corteva spinoff is part of a long-tail plan by DowDuPont to separate its sprawling business into three separately traded entities. It already divested one, materials science specialist Dow, in March. (Dow is now on the S&P 500.) Corteva is slated to go its own way on June 4, leaving the specialty chemicals business inside the current DowDuPont. That date, before market open, is when Corteva will join the S&P 500.

After-market investors seem to approve of this shake-up, if not enthusiastically. Shares of all the companies moving to new S&P index homes are trading either flat or slightly up tonight, save for the modestly declining Pioneer Energy Services.

Oh no, Inovio

Inovio Pharmaceuticals stock is down by nearly 4% this evening on some discouraging news about a key partner. Inovio said in a regulatory document filed after market close that MedImmune, a subsidiary of pharma giant AstraZeneca (NASDAQ:AZN), will withdraw from certain research activities in which the two were engaged.

Inovio and the AstraZeneca unit had a license and collaboration agreement to develop several cancer treatments. The latter company held the rights to codevelop one or two potential DNA-based cancer vaccines. The evaluation and development of a third cancer treatment candidate, MEDI0457, will still be shared between Inovio and MedImmune.

For obvious reasons, cancer is a hot area of clinical study these days. That's a clear advantage -- however, Inovio has no products on the market yet. Being in the pre-revenue stage makes it dependent on development, so an announcement like this isn't being received well by investors. That said, it's good that all in the Inovio-AstraZeneca partnership is not lost -- it is still hanging on with the development of MEDI0457.

Nevertheless, the bears are really slashing at Inovio tonight. The stock is trading down by nearly 18%.

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