Billionaire investor Stanley Druckenmiller 's top three biggest holdings at the end of June were all health-care stocks and he also invested back into one of his favorite artificial intelligence plays, Microsoft , according to a regulatory filing. The former lead portfolio manager for George Soros' Quantum Fund, who now runs his own Duquesne Family Office, hiked his stakes in Teva Pharmaceutical and biopharmaceutical company Insmed last quarter, making them his fund's second- and third-largest holdings, the filing showed. Clinical genetic testing company Natera remained Druckenmiller's top bet, worth more than half a billion at the end of June. The legendary investor, who has never had a down year in the markets, took a $100 million stake in Microsoft in the second quarter, after exiting t

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